Just thought I would share a bit of my recent experience in installing OME 885 springs on Bilstein 5100's. When I ordered everything, I did not get new bushings for the top plate and upper strut mount. I figured it wouldn't be a big deal, since I could just re-use the stock pieces.
So, I installed everything, but within a day or so, I started hearing a aggravating, high-pitched squeak/screetch every time I rolled over any sort of bump in the road (no matter how small a bump it was). It definitely sounded like metal-on-metal... no bueno.
I looked at the top of the strut assembly, and noticed that the shock piston was not centered in the top plate, and the top bushing (just below the top nut) was nearly hanging off the top plate on one side.
So, the next weekend, I pull the strut assemblies back out... which was a complete pain in the ass, because the top bushings were catching on the top mount, not allowing the struts to drop out of the mount... so I had to put the strut compressor on the springs while the struts were still on the truck (don't try this at home, kids... danger!), and pull the top nut and bushings off so the strut would drop out of the mount.
Anyway, this is what I found:
Top plate... yeah, that little off-center notch should NOT be there:
Shock piston... not exactly what you want to see on 5-day-old Bilsteins:
So, today, I installed new top plates and new bushings, and now everything is groovy.
If I had just spent the 20 freaking bucks and bought new bushings in the first place, it would have saved me about 6-8 hours of work and about $120 on new top plates.
NOTE: My truck has about 90K miles on it, so the bushings were pretty worn out. They just allowed the shock piston to move around just enough to wear that notch in the top plate and shock. The new bushings are much stiffer and made for a much more solid mount.
If you have a NEW truck (with, say, less than 30K miles) your bushings may very well be good enough to work without any problems. But hey, if you're going to drop several hundred bucks on new suspension, what is an extra $20, just to make sure you don't encounter the same problems I had.