bently manual says my 90 multivan 4speed manual trans will retain 1.5
liters of gear oil after i drain it.

1)how do i convert to synthetic with all that mineral oil left over?
2) if i get mt-l(gl-4) instead of mt-90(gl-4) any problems or is it ok?
and
3) that tool that's made w/ 17 mm bolt, some say to turn 2 nuts onto it
and jam them together---where on the bolt? what's the purpose?  i don't
remember seeing jammed bolts on "Stan's tool tour".

thank you in advance,
chris c
wisconsin westy