Hmmm...it makes sense that not all servers allow custom cars...maybe that could be set in server settings.
But, since you said that some of your friends see your custom cars too...i wonder...how did you setup your custom car? The way Dr.Feelgood described at the beggining of this thread? Or how?
I see other custom cars...but others said they dont see mine...on same server...so either only a few can have custom cars on some servers...or i dont have them set properly?! (btw...i see my custom cars...and i also have all ports needed for the game open in my router...so dont know what else could cause that)