Arch, I didn't keep the list of Porta-Trax owners, was very informal cottage business that was more fun than anything, I doubt if there is any 5-year old carpet around anyway. Moreover, I changed the Ozite formulation at least twice, some of it was not very good at the beginning.
Here are some pictures of the throttle mod: It's ever so simple and costs less than a dollar. Works great though. You just dial in the amount of throttle you want. This first attempt was a little messy and you have very little clearance on the battery pack; that's why I installed the "puller" tab at the end of the battery pack, as the pack sticks a bit when you press the release button (planned also, because kids will inadvertently press that button and the penalty for doing so should be power off, not 4 AAA batteries all over the floor!).
I used a brass knurl nut to embedded into the transmitter casing to receive the large plastic screw, which is easy on the fingers (and I don't like metal-to-metal around R/C).
You need a Dremmel tool to cut away the groove for the brass knurl nut and I secured the nut with CA. I also cut away the small protruding plastic piece on the trigger, so that I could still get full throttle if the plastic screw is turned all the way in.
http://img34.imageshack.us/img34/4550/picture005l.jpg