Sorry I haven't been back to answer. I've never put any additive in it, it's been mine for the past 8k miles and several oil changes. I'm pretty sure I've used only Rotella, dino and synthetic since I've had it.
A lot of people say that you won't have clutch slipping issues if you stay away from oils with "energy conserving" on the API label. Generally this means 30wt and under. I've personally never had a clutch issue running 10W40 automotive oils or HDEO, and I know I'm not the only one. So far as...