My manual for an 02 Forester says to use a sealant on the rear diff plug. It calls out some special stuff. What is it? Are there any substitutes?

yep, the RTV type stuff you'd use on cam cases, oil pump, separator plate will work fine.

Indian Head Gasket Shellac Compound will also work.

I never used it (3x) and never had any leaks

I never used it (3x) and never had any leaks

me either....shhhh, don't tell, i didn't want to start one of "those" debates again. if this guy wants to, no harm in a little gunk on his finger and threads.

^^^^ + 1, shhhh...

I use liquid teflon "tape" for stuff like this, seals but luse so can be taken apart easily....most auto stores dont carry any more but plumbing aisle at Home Repot, etc. has it