Thanks again, http://pastebin.com/bkCanSgC
I should mention, and should have explained better the first time, the cars I have replaced, I have done so in Lua, not modding the gta3.img. I am connecting to my server on this PC, and all the script currently does is replace the car dff/txd's.
EDIT: I've had a bit longer to experiment with this, and have tried it on a different PC with a clean GTA install, with the latest nightly. Same problem occurs, but I have noticed, the cars don't completely lose reflections. I tested it at night in-game, and things like street lamps, other car headlights, airport lights etc, all cause the cars reflections to work. It's just as if they ignore sun/moonlight. If I need to provide any more details, just ask.