There's been several 68 dt1 threads lately so just sharing an observation that I don't recall if previously has been posted.  When restoring DT1-00490 I noticed it had a brass crankcase breather fitting, so just an assumption brass may have been used before assembly line changed over to the familiar white fitting.  My next lowest VIN engine is DT1-0151x and it has the white breather connection.  If this is correct just creates another challenge when restoring these vintage jewels!!   
Curious if Capt. Dave's very early #51 or Shawn's 0500 has brass fitting?   Others?
Regards

 
 
 

This is from VIN # 0074xx and is white nylon…

 

correction to the above VIN #

 
 

Both of my bikes are white nylon. Early bike with no VIN appears to be between VIN 2800 and 3300 from some detective work…so interesting that 074XX is nylon as well as many others. No pattern emerging yet. Wondering if the brass one was a preference of some mechanic working on it back in a day? 

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I have an unrestored 68 DT1 that was just three bikes behind yours, coming down the assembly line ... # DT1-00493
Mine also has the brass fitting!
I'd say that pretty much proves the brass breather was an original piece on these early bikes, and not a replacement part.
Good eye swm! . . . haven't restored my bike yet, so I never noticed this before.

 
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For the curious of mind . . . the yellow "plug" is a mice deterrent!  LOL

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Good spot that ….

my 01012 is white nylon ….

cheers
T1

So... any one go looking for the brass breather plug? Them nylon ones are very easy to break when dis-assembling..
Sneezles61

"Them nylon ones are very easy to break when dis-assembling."

And the ones that Yamaha supply now don't really fit properly either! 

Another use for a T post hot wire clip