I recently split my '74 360 motor apart, 15k miles and 50 years after it left the factory.  It's been running great but it couldn't hurt to freshen some bearings up and give it a once over.  I was curious about the condition of the ancient sealant at the center case joint as well.  Upon disassembly I was surprised to find two stroke oil had been pushed forward into the hollow cavities adjacent to the crankcase near the front engine mounts.



If you've never had yours apart, it would be prudent to open it up and freshen the goop sealing the case halves.  If it leaks oil I'm sure it will leak air as well.

Very common place for an air leak on a DT360.

Not uncommon to see oil in there, curious though, even on a modern bike fairly common, and not showing leak any where else  on the case half , always puzzled me 

I have a habit of pressure testing before disassembly...  several 360's and 400's I've worked on have an air leak around the front motor mount for some reason. 

Here's a DT360 that had a pretty significant air leak... over 1 psi per minute....  hard to see but spraying copious amounts of soapy water around the front motor mount resulted in large soap bubbles forming around the upper mount bolt hole.  I outlined in red just outside the bubble.