Harman Kardon Rabco Turntables/HELP

Some years ago Harmon Kardon produced the linear tracking turntables.My question are they any good and worth the effort to acquire and set up.Also what cartridge MM is recommedned.
If I remember right there were 2 models. I had the cheap one & a friend had the more expensive one. His seemed pretty good however mine had a terrible problem with rumble.
I have had HK rabco tables both a 7-[silver] and an 8-[black].Both had grado carts which worked well with them.Rabcos work well but HAD TO BE MAINTAINED! Dust would make the arm go akimbo not a pretty sight or sound.Must be in a clean lab environment as dust is a terror to one
I have one, and I agre the rumble was horrible. The motor is tiny, about the diamater of a silver dollar. The spindle and bearing are also light weight. That said, I used alot of lead shot , a Sorbathain record mat, and a ton of sorbo wraped in strategic place, and the sound shaped up fairly good. If you get one for $50, it is ok, I wouldnt put a lot into it. One other thing, if you can get the Rabco arm adjusted to where it is not weaving back and forth (over and under adjusting contsantly) it can sound good, btter than most mid fi tables once you get rid of the rumble. You are better off spendng money on a good Rega P2 used than the HK, sorry but that is the truth!