More of everything than in your worst nightmare!! Once you get everything clean and tight I think/hope that all your problems will go away. E38's are VERY volts sensitive so a couple of bad joints or a dirty earth will really throw spanners in the works! Beware that code readers can be mislead by bad connections so make sure the simple stuff is good B 4 you spend bulk $'s on faults that don't exist.
Good - Fast - Cheap: Pick any two.
E23 735i; E32 735iL (X 2 - 1 Alpine White and 1 Glacier Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E30 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i