4kcsq struts upgrade and other Q's

["Mausoof, Saqib" <SMAUSOOF@Allstate.COM>]

Hi all,
Time as come to upgrade the rear struts on my 87 4kcsq. I have a few
questions regarding the upgrade.
1) What is OEM on this car?
2) I had the fronts upgraded a 2 years back, should buy all 4 now.
3) Can I slip KYB gas inserts on the OEM struts?
4) How hard is it to install inserts? I have done it on an old Mercedes
before, special tools needed?

While I am at it, my 4kcsq is emitting a very high pitched screeching noise
form the motor. It starts after the engine warms up a little, and is audible
when idling but seemingly vanishes when the go over 2000 rpm. Could be a
vacuum leak but I can't point it. Any advice would be appreciated. 

Thanks in advance
Saqib Mausoof