Interestingly - engine 8582 is the same as yours and has no clip. Also has front numbers stamped that are close to engine number. JGersh numbers are also in the ballpark, and yours is close to your frame number. 
 

JGresh wrote: "The more interesting part though is the first change notes the elimination of a right side circlip at the same time."

I am not nearly as familiar with the 250/360/400 models...  But I'm pretty darn sure that:

- Early 250's did not have a circlip to retain the RH clutch side crank seal
- Later 250's had the circlip to retain the crank seal in the RH case
- Service bulletin reference to eliminating a circlip has to do with the transmission, not the crankshaft...  most likely the transmission input shaft bearing on early models had a circlip on both sides...  replaced by a cast-in boss on the inside of the right case on later models. (Maybe someone who knows more than I do about the 250's can confirm?)
- Enduronut and/or DEET probably know all the details of these changes/updates/improvements including the exact day/time it happened and the names of the assembly line workers who assembled the first examples.

(Well, maybe I'm exaggerating a little on that last one.)

If this was my bike I'd be tempted to get a matching case set...  Especially since Yamaha obviously "matched up" the early cases as evidenced by the number stamps...  this is exactly what many manufacturers did.  On later bikes, manufacturing tolerances may have improved to where matching and serializing halves wasn't needed?  I just personally feel better about a matched pair.  Many available on ebay for reasonable prices.

Noticed two more stampings here: just thought I’d post out of curiosity to see if they have any significance. The first is on the rear underside of the right case. What I thought was odd is that the front of the right case is stamped 3265, the back 3290. Second is a “C” on inside of exhaust port. Have not spilt cases, waiting on parts and tools yet.  

Was any more progress made?   I'm just curious. It doesn't have any bearing (pun) on anything I am currently working on.  But to have gone through all that research, discussion and speculation and not have the issue resolved is frustrating.


Never mind,  resolution is here : dt1 up running