Thanks for the responses! Yeah, don't fix if it ain't broke.

In some other car forums there are reports it "saved" them... but none here(?). I guess it helps (temporary?) if something is wrong with the transmission already.

I wonder what causes other (older) cars to suffer from transmission slip, bad shifting etc. I can see some wear on the gears, but that shouldn't cause slip, right?

'91 LandCruiser