I agree, that makes a lot of sense to have the dual lip on the flywheel side as well. It looks like the set I ordered has a single lip for the flywheel side, so I'll look into getting some different ones.

I just picked up my tiny little $150 bag of parts from the local Yamaha shop. Wish I’d’ve known about the IT crank seal. I just got the standard CT1 seals. Oh well.

Enduro 125 and 175 engines came with a single lip seal on the ignition side.  I hesitate to say "all" but pretty sure it was all of them from 69-71.  Same crank seals too through the years too...  none of the goofy size... change dimensions every couple of years...  made of "virtually unobtanium" crank seals the bigger bikes got. 

many YZ125, the YZ175, and IT175 got proper dual lip seals on both sides of crank. 

The single lip obviously works...  until it doesn't...  the dual lip is just better and worth the extra dollar or two. 

I've been thinking about this, and that left side seal is going to be running dry on the outside portion, so I can understand why they originally made it solid on the outside, and only put a spring-loaded lip on the inside, which is always bathed in oil and gasoline.

However I do understand the logic of having a spring-loaded lip on the outside, to maybe help prevent air from sucking into the crankcase. That said, I think I'm going to go with the seals I ordered, which should be arriving today. This bike is not going to be ridden that much, plus if I ever had to replace the left side seal again it's FAR easier than replacing the right side seal.

I also had absolutely no sign of oil leakage into the ignition area, and I think my main problem was transmission oil sucking in from the right side, as well as two-stroke oil leaking back into the transmission. I think that right side seal really takes the brunt of abuse, both from the crankcase and the transmission, and it really was shot.

I finally found them! I knew I had the service manual and owners manual, but not using them in decades, I had no idea where I put them. I moved four years ago, and I've been looking through boxes and all over the place, it turned out they were under a stack in a bookcase in my home office 

Tom P I hope you don’t mind if I use your thread here, but we are doing the exact same bike and we are doing the exact same steps.

I have placed the new o-ring in the groove on the splined shaft end of the crankshaft and I am trying to reinstall the sleeve spacer. It seems like way too much of an interference fit between the O.D. on the o-ring and the I.D. of the sleeve spacer. Am I supposed to use a hammer and tap that sleeve over the o-ring? I’m afraid it may try and roll out of the groove and be ruined without my even knowing. I attached a YouTube link as well.
 

youtube.com/shorts/itne0Kjg1fE?feature=share
 

I've read elsewhere that it's better to install the seal, then install the sleeve. Either way, make sure the little O-ring and the interior and exterior of the sleeve are well-oiled. I know when I was pulling my sleeve off, it was a tight fit on that O-ring, even with the old O-ring. You might have to find a large socket or something that you can use to tap it over the O-ring. In fact I just checked and a 20 mm deep socket would work perfectly. Another thought, it might be a good idea to rotate the sleeve as you push it over the O-ring. However both ends of the sleeve are chamfered internally, so I really don't think it's going to push the O-ring out of the slot.

I got brave and tapped it on using a socket like suggested. Very tight fit. But done and seal is installed. 

Got the main seals a little while ago, and have the left one installed, and the stator and flywheel back on. Also a new seal for the kickstarter opening in the right side case.. The crankshaft O-ring and clutch pushrod seal aren't coming till early next week, so that's about all I can do for now.

Been reading through the owner and service manuals, and a couple things are interesting,. They recommend 90 octane gasoline, and for holding the gears while torquing the clutch and primary, they say to roll up a rag and stuff it between the gears. They also say to put Yamaha Bond #5 on the mating surface of the right side, then put the gasket on, then put Yamaha Bond #5 on that before putting the case on. It seems like most threads I've read here and elsewhere have people just using grease, oil, or just the gasket, but the manual says use Yamaha Lube #5 or the case will leak. So I haven't decided what I'm going to do with that yet. I do have the gasket.

Because the right side isn't together yet, I just put a strap wrench on the flywheel and was able to torque it down to spec. Also ordered a new chain, the old one is just too rusty.

Octane rating measurement changed over the decades.  Gas wasn't "better" back then...  it was rated different in the US.  RON was only used back then.  Now average of RON and MON.  Other countries still use only RON...  probably because it is a higher number.  The MON test method is "harsher" and it's generally agreed to be closer to emulating real life auto driving conditions. 

Modern regular grade 87 almost certainly has a RON of 90 or higher....  probably 92 or 93 for most brands.

The manuals sometimes have a convoluted and misleading...  or even an outright wrong...  way of describing things...  Generally the Yamaha recommendation is to put #5 on the cover or case surface and #5 on the gasket surface that contacts the cover or case.  This is because #5 works like a "contact cement".  You coat both surfaces and then stick them together.  In my experience and opinion, Yamaha never intended to have sealer on both sides of cover gasket...  it's used one side to hold gasket in place.  But many of us don't use the contact cement and it doesn't leak.  The grease usually allows you to remove the cover without destroying the gasket. YMMV.