Yeah, my 98 was having clutch slippage, lower MPG, and it backfires on shutdown. I thought it may be from my inept wrenching skills.... After reading this thread, and due for an oil change I decided to send the T-6 synthetic to the bench.
Oldfeller--FSO wrote on 06/25/16 at 17:19:13:
It also seems to be able to be reversed easily. (which is a good thing)
Yep. Filled it up with Mobil 1 4T 10w-40 - $10 per quart
Took it on three tank long test rides(last one today) - no clutch slip, improved responsiveness(torque), and my MPG went up from about 45 to 52 MPGs (not a good test, as these tests were entirely on twisty, bucolic canyon roads with no braking, but I enjoyed the test
)
So I'll stay away from T-6. I still have about 2 quarts left, I'll just use that to top off the my various internal combustion engines when they need it.
Oh, and it still backfires on shutdown