MT-1 Gear oil question

doghead said:

Synthetic in the trans, have proven to seize 2nd gear to the shaft.

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Ok, I know I'm reviving an old thread, BUT I really wanted to understand what this comment meant.

For clarification - which lube / synthetic in particular causes 2nd gear seizure? a synthetic 80/90 GL5? 80/90 GL5 MT1?
But, above has been mentioned some straight 50W oils, some intended specifically for manual transmissions. What about synthetic versions of that? What about "Delo synthetic transmission fluid 50" ? Will that / does that cause 2nd gear failure?

I've been doing a lot of research on here about fluid for transmissions and transfer cases, and been reading the discussions between GL1, GL5, GL5 MT1, SAE 50 meant for manual transmissions (and synthetic versions of that)... which is why i'm here reviving old thread

Again, I respect your opinion, I'm just not sure to which product(s) your opinion referred

the case against gl5 is the EP additives can attack the yellow metals at high temps, and thusly drivelines with brass/bronze are generally gl4 rated (my old bmws spec gl4 for the same reason and redline mtl is mothers milk for them for shift quality, but they can also deal with atf for cold weather use, doubt the old spicer would like that at all)