I have 750il -1991-E32.

1) My rear shock absorbers are leaking oil. So, I am trying to replace
those. But it seems quite expensive for the 2 pieces. So, I am thinking
replacing them with non-self-leveling aftermarket shock absorbers. I once
read that I have to do something with the electrical circuit not to
complain/malfunction/malwarning when I replace with those of not self
leveling.
Would anyone send me the tech giude for the replacement procedure? if
possible, photo might be good or any web link which shows the procedure all.

2) Another problem is very stiff break pedal. Usually OK, which means I have
soft hydrauric softness of berak pedal when I press the pedal. However, some
times( I can not tell the exact situation of occurring), I have to press the
break pedal really hard to stop the car. Then ABS kicks in. It just like I
am stopping the car by mechanical break rather than with hydrauric power.
So, I consulted mechanics and their opinion is varied as below.
a) I  might need to lubricate the master break cylinder --?
b) I might need to resurfice the break disk smoothly
c) I might need to replace break accumulater ball.
d) break oil air breeding.
Shoul I do all of these 4 or any one? Even others? What is your opinion?

Thank you in advance.