How much strut side to side movement is too much?
 

I'm working on my '01 Boxster S with 75,000 miles. If I grab the front strut just below the spring mount, I can move the front right strut in & out approx .035" based on the location of the dial indicator. The front left has about .030" movement and the rears are each about .005" following the same process.

The movement in the rear cannot be felt by hand, while the movement on the front right seems like too much.

http://mreimler.smugmug.com/photos/i...-2rrmFkf-M.jpg

The upper strut mounts are tight and there is no movement at the top of the strut shaft where it bolts to the upper mount. There is no leakage from any of the struts and the suspension is original to the car.

So the questions is, is this too much movement? Are the struts shot?

Wow. Excellent investigation I must say. It SOUNDS like a lot to me and I know what .035" is. Do you think the movement is the lower ball joint or inner bushing/ mount? Does your car have any rattling while being driven?

Using a 24" pry bar I couldn't get any movement from the ball joints or bushings. I do get a clunk from the right front over bumpy roads at low speeds.

Anyone?

I'll also ask which Bilstein strut is most similar to the OE S suspension. Sport or HD?

If I'm reading this right, you are able to push / pull the strut sideways by .035" (I can't see where your dial gauge is mounted to).
The strut shaft is bolted to the upper strut mount by the M14 central nut and the strut mount is bolted to the chassis by the 3 nuts you say are tight. The strut mount itself has a bonded rubber insert which can and does break away with age. Not an expensive item, but quite a lot of labour to replace.
The only other component up there is the strut bearing itself which can rust and wear and cause a knocking on rough roads. I'm willing to bet that these are your culprit. If you have the Bentley Boxster manual look @ page 40-5 for details.

Using a pry bar on the suspension bushes will reveal nil movement, even when they are worn. With 75,000 miles on your wishbones / drop links etc., there's bound to be some wear which shows up as a knocking or rattling over rough surfaces.

I replaced my 50,000 mile S suspension with PSS9's a few years ago and fitted new top mounts too as a precaution - the old ones looked OK & the bearings were fine, but I live in a warm dry climate which always helps....
Pity you don't live closer or you could have my old suspension & mounts cheap!