the teflon mouse tape works great! i have no way of measuring the thickness of it but it looks pretty thin. thin enough for it to be translucent when working in a well-lit room. i went ahead and placed two layers (long strips) of the tape on the inside of the stock at the 12 o'clock, 3 o'clock, and 9 o'clock positions. did a test fit and noticed there was still a little play coming from the bottom channel of the stock, where the retention pin locks the stock into the 4 positions of the tube. so i went ahead and placed one layer of teflon tape just to the sidewall of the lower channel of the stock (to avoid messing with the retention pin), and did another test fit. worked great! absolutely no left-right wobble and slides really smooth. there is still a little front-back wobble, probably due to a small gap where the retention pin locks into the tube... but i'm ok with that.
over all, VERY pleased with this inexpensive fix for the stock collapsible stock. this will hold me over for awhile before getting a magpul. haha
thanks, again, for your help and suggestions, TM! time to go shoot.