A square wheel rollin' !!
The STP is really nothing more than very thick conventional oil that has a dose of zinc in it. Zinc is good for reducing wear in metal-to-metal friction areas such as gearbox, solid cams, etc. Most modern oil has removed it because of issues with EPA/emissions.I'd still be really worried about running that STP in a motorcycle engine tho. Hopefully it won't have any effect on the clutch plates otherwise you will start to feel them slip and end up having the replace them.
From what I have been able to find , the STP will increase the oil's viscosity by about 10W , effectively turning my 10W-30 into 20W-40.
Moly is the "bad guy" additive that is slippery but messes with wet clutches. Not an issue as far as I have been able to find online, the STP doesn't use it.
Haven't looked at the MSDS sheets in a while, but I did my homework before using it.
I find it interesting that you didn't feel a difference in your trans when using Rotella T6 5W40. What oil were you using before you started using the Rotella T6?