Ok I've read multiple threads with no luck. I have a vulcan 900 but it seems to be the same design. I have split my engine, cleaned everything, replaced oil seal, mechanical seal, and impeller fan. This has been MULTIPLE attempts. The first time around i was replacing my clutch plates because my clutch was slipping. So I removed the RH crankcase cover and replaced em. I never touched the impeller fan. I'm assuming my trouble started by opening it up to air and things just started going wrong. Cranked the bike back up and i was leaking coolant out of the weephole. Upon reopening the cover and reading the manual, which told me to replace mech seal, that is what i did. Then after starting up again my oil and coolant mixed. So i replaced the oil seal after splitting the case (quite the task) Then the mech seal again, then the impeller fan. My point is that i feel like I've tried everything, and with a new oil seal, mech seal, and impeller fan, it is still coming from the weephole. And it's practically pouring out. I have been thorough and careful but it is still going to ****. I'm hoping to get some insight or maybe im missing something. I know there were some gouges on the aluminum where the mech seal seats (because i pryed it off) but i used a little extra rtv to fill the void when it seated. Im pretty competent in the mechanical field, and i never considered posting on here, but im honestly pretty desperate for an answer here. I'm confident the issue is coming from the mech seal mating surface or the impeller fan mounting bolt. It's definitely a dumb design to have such a fragile wall between coolant and oil.

I'm about ready to pull the crankcase again and inspect after about 15 minutes running the engine to find where damage couldve occurred. To be clear, i have replaced the internal oil seal, the entire spring assembly behind impeller, the seal that goes into the back of the impeller (which i think is the 9mm oring people have mentioned), replaced the impeller fan, and the bolt and washer. Tq to 87 in lbs. Where have i gone wrong?!
If i didn't know better, i wouldve filled the weephole with aluminum bondo to stop the leak(which i considered) but i know that it would just decay the oil seal. Coolant alone is getting in to the weephole but how do i stop it? Should i use quick aluminum bondo to repair housing for mech seal, or anything i might be missing..Any suggestions would be greatly appreciated.

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Don't have a lot to offer, just shots in the dark which you've probably thought of already , or are just deep in left field.

Double check part numbers.

Gasket out of place? Gasket surface was completely clean and flat? Seal pressed too deep/shallow? On the 750 I think there's a lip and it just presses in flush.

Those gouges? Check ebay for a used case section? Product called Belzona might help, if it's still available, and if you're going to try filling the gouges.

Groove worn on the shaft?

Alternative to aluminum bondo ... Thread the weep hole for a bolt, then it's removable. If you do that, does water still get into the oil?

Alot of good points and possibilities and thanks for the input. There are gouges around the mating surface where the lip seats. I filled in with rtv, then squished it down, but pressure couldve knocked out a path for the coolant to come through. Makes me wonder.. if i could use the aluminum bondo to "weld" the seal into the casing. Otherwise, i would be looking at completely replacing the right crankcase, and to be honest im running low on faith and funds. That has to be the problem. Im pretty worn down on ideas, and if i threaded a bolt onto the weep hole that could be a temporary fix, until the coolant ate away at oil seal. Once oil seal gives, my coolant and oil mix, or i leak oil. I think thats the next best thing (mating the edges of the mech seal with crankcase