Is there a similar product for the manual transmission?

Recommendations for other products greatly appreciated!

Don’t know what that is, but if you intend to add that to the transmission oil I would say no.
The repair of the transmission main shaft seal is a few hours time.
I would avoid anything that goes in.

None of these seal repair products are worth the time or effort. Save your money.

The only permanent fix is to replace the seal.

A bottle of magic fluid costs about the same money as to actually buy a replacement seal.

That is what I would do, but then I have rebuilt a couple 914 transmissions. Someone with fewer tools might want to avoid the work by pouring in the sauce. Besides simply a waste of money, what bad things will happen? I should add that my son is a professional car restorer and he also votes no for the snake oil fix.

Yeah, Dropping the engine just isn't hard enough to justify a shortcut. If you don't have the tools to do this, you'll need them soon enough owning a 914 anyway. The biggest danger is, "while I'm in here, that clutch has seen better days..."