I had the M47 five speed rebuilt for the second time last spring (@340K miles)by a well known, long-established transmission specialist. When I dropped it off, I asked what kind of lubricant he was planning on using; he told me he would use a synthetic automatic transmission fluid, and that's what showed up on the repair invoice when I picked up the car. Except for a few issues with a leaking rear main engine seal, all seemed to be well for a month or two. Then, after a long stint on the highway, I started getting a slight grind when I downshifted from 5th to 4th. It didn't happen consistently, but enough for me to take note. Lately, since the weather has cooled, it has been noisy in 3rd 4th and 5th and a little balky shifting in the morning, which led me to believe what I verified today when I drained it to refill with Redline MTL. I first made sure I could loosen the fill plug, which took herculian strength and a breaker bar.... Ugh.
When I pulled the drain plug I immediately caught the scent of hyphoid gear oil, probably 80 weight which began pouring out like honey. It was very clean, and the drain magnet had some, but not much metal shavings. My question is, what damage, if any, has been done? I've driven about 6000 miles with the gear oil in the box. After the change to MTL, it shifts like butter and is very quiet. I'm going to let the rebuilder know how disappointed I am with him, but I'd like to know if I'm going to be stuck with yet another rebuild soon, so I can start looking for someone else.
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