+1 - just use something and you'll be fine. I work on enough bikes where the grease is so old as to be non-existent and, even then, things are usually fine (but run much better with new grease). I'm far from an expert but I think there can be a bit about the base of a grease having a poor interaction with greases with different bases. I just take this to mean when overhauling something with bearings, clean out the old grease really well. Then, no worries. Personally, I use either Park (have an old tube) or a Teflon grease...the latter mostly in my winter bike (in Minnesota).