RE: headlight. A picture would be helpful. I suspect you have Euro headlights. Search for that term, maybe you can find a pic on eBay or somewhere.
You can order Euros from Puma:
http://www.puma-access.com/hella/hella.html
Did you get the license or truck owner's name? They will pay if you report it, o/w your out a few bucks I suppose. I always dread catching a rock on my Euros. On the W124 Euros run almost $250 a side.
RE: heater problem. Welcome to the gremlin called Mercedes Climate Control!
You probably need to have some diagnostic work done, if what you say is true. The heater fan running up and down in accordance with engine speed, is well, I dunno, strange to me, unless the battery voltage is varying a lot.
There is a mono valve that usually sticks closed, its possible yours is open all the time allowing hot coolant to circulate. The climate control uses a module that is an analog circuit assy, connected to the mono valve, a small circulation pump, and the dash mounted control board which lies behind the push buttons. The latter items is known to have relays that stick or fail to make contact and it has solder connections that get fatigued and need to be resoldered.
The CC system is a system takes a bit of work to understand before any troubleshooting will pay off. Shotgunning components is not recommended unless you have access to known good testing modules. Goodluck!