Just about to take forks apart to add a spacer to a set of revs and as I’ve various engine, clutch and gear oils in the shed, I’m wondering can any of these be used in place of the proper fork oils.
There’s 5w/30 semi synthetic, 5w/30 fully, 15w/40, 10w/40 semi, 75w/90 semi

Brand is irrelevant, its the specifications that matter.
A few years ago, i filled a deore brake with 3in1 oil.
Nobody died, in fact it’s still working fine.

Brand is irrelevant, its the specifications that matter.
A few years ago, i filled a deore brake with 3in1 oil.
Nobody died, in fact it’s still working fine.

5w/30 fully will be a good choice for the lowers.

Cheers, and for the red rum?

The same.