86 240 sedan/ manual M46_118,000

I recently drained the tranny on this car. I drained fluid and removed the overdrive pan cover/gasket. I cleaned off the old gasket residue on all surfaces along with other residue on pan cover.
Since I didn't have a new gasket I dupped one from old one with 1/16th" gasket material,(very carefully).

I then assembled everything using gasket sealer on both sides of gasket. I evenly torqued all bolts in order without using a torque wrench.(access)
I refilled with MTL Redline and took her for a spin to work through tranny.
Checked level of fluid with car level and everything seemed cool.

After a few weeks I checked the level again and noticed the leak around O.D. pan gasket area(slow leak). I checked bolts and re-torqued again (carefully) afraid of over torqueing, cleaned area up and checked again a few days later to find the same problem.

I checked with a local brick mechanic who told me it had to do with the thinner viscosity of the Redline???
What to do next??
If I do pull O.D. pan cover without draining tranny(to try new gasket), should the O.D. section be closed off,fluid wise? I don't want to lose the precious Redline.

Any ideas much appreciated
Chapster out