I used to use 85/140 gear lube and ATF mixed on my inboards, Im sure you will get a hundred different answers and maybe Clegg's oiler prefers one over another - he should chime in when he gets back from Kems.
Take STP oil treatment and mix it with enough synthetic motor oil to thin it out and make it flow. I have never worn out a shaft or liner using this mixture.
Just wanted to see what some of U are using one of the tunnel hull guru's (Gabe of Stump Fab)
reminded me of what we use to use 2 parts Marvel Mystery oil to 1 part STP