Sounds like the master has died. Easy rebuild. Take photo's as you disassemble. Take the unit to a good local specialist. They will have seals on the shelf (OK they do here). May as well do the slave too. Same general instructions. Morning job -Drive in the afternoon.
Good - Fast - Cheap: Pick any two.
E23 735i; E30 318i; E32 735iL (X 2 - 1 Alpine White and 1 Glacier Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i