Oil leak from crankcase mating

[chuckt52]

New here so, Howdy!
I've got a '79 750k that has been rebuilt.
Story goes:
2 winters ago, I did a complete refresh of a bike I've slowly been building up.
The motor was taken out, new chain guides were installed, new rings, and the head was rebuilt.
Last summer, I failed to adjust the timing chain properly and locked up the engine...
That weekend I took the motor out and found bent valves on the intake of cylinder 1 and I believe it was the exhaust of 2.
The chain had jumped the big sprocket and locked up on the intake/exhaust chain.
I split the cases apart, to install new chains, new guides, and all new seals.
Back on the road for the rest of last summer. Peachy.
BLAH BLAH BLAH

The issue is that I have a slow oil leak directly next to the main seal (drive gear)
Before any lower end work, there was a ton of gunk built up around the main seal telling me there has always been an oil leak, but the grime just concealed it.
I just assumed the seal was leaky.

I'm trying to figure out what I don't know.
The leak is minor, but I don't like having to worry about oil on my rear tire.
Am I getting too much crankcase pressure?
Maybe the wrong oil? (Been using high mileage 10w40 full synthetic)...

Attached a few pics showing the cases prepped before assembly, and the last pic was one I took from the bushes waiting for a tow truck on Memorial Day 2023.

 

[Loose Chain]

there was a ton of gunk built up around the main seal telling me there has always been an oil leak, but the grime just concealed it.

That build up you are referring to was probably road dirt mixed with chain lube that always builds up behind the cover. What type of sealer did you use on the case halves? Also the oil you are using, is it automotive 10w40 synthetic you are using or motorcycle specific? You shouldn't have crankcase pressure if you have the breather hoses still connected to the airbox.

 

[chuckt52]

That build up you are referring to was probably road dirt mixed with chain lube that always builds up behind the cover. What type of sealer did you use on the case halves? Also the oil you are using, is it automotive 10w40 synthetic you are using or motorcycle specific? You shouldn't have crankcase pressure if you have the breather hoses still connected to the airbox.

The crankcase pressure was just a shot in the dark, and I used Loctite 518 flange sealant. I dont think the cases are the issue.
I assumed 10w40 was 10w40. They make motorcycle specific oil?? HAHA

 

[Loose Chain]

Ya you don't want to use automotive synthetic oil, the clutch won't like it at all. So if it's automotive synthetic, get it out as quick as you can.

 

[chuckt52]

Ya you don't want to use automotive synthetic oil, the clutch won't like it at all. So if it's automotive synthetic, get it out as quick as you can.

Good to know. I've been running the same auto synthetic 10w40 for years. My started slips occasionally, but I assumed the rollers were worn, or the synthetic was messing with it. The bike needs an oil change anyways so Ill swap over to a motorcycle approved formula. Thanks!

 

[brettp]

The owners manual for ALL metric bikes says oil must be JASM (?) rated.