One of my lexus rear struts (well coilover type strut) had a film of oil. Just enough for a dirt coating, the other was clean. The leak was down to the spring seat. which is about an inch above the bottom of the strut.. I read that this is a borderline case for replacement, some leakage is acceptable per Toyota. I think 1/3 of the length is ok. I did replace both though, the old strut isn't crazy broken if you push it in or out. It does feel a bit tighter in the rear though. Almost thinking of doing the front too at 100K, but they aren't leaking.