Mitsubishi Repair: 90 Eclipse 2.0 front end shimmy/shake, shimmy shake, wheel bearings

Question
Hello,
I am baffled and so are the mechanics about the front end shimmy/shake at approx. 45 mph...levels out then 60 mph range, it starts again. Left slight turns makes pull to left and shake increase). All tires have been checked/changed, wheels too in case they were out of round, multiple balance and alignment at 2 different shops, all motor mounts replaced, all belts replaced including timing belt(s), rear end checked, struts/shocks checked and etc, auto.transmission drained, flushed and filled (transmission replaced at 65,000 miles - now has 93,000).  At one point a mechanic said a special Mits trans.additive was needed on that model???have you heard about that one?
Anyway, it will do the shimmy/shake each and every time at the above speeds and there is no historical point of reference as to when it began, i.e. no shop visit, no breakdown, no other symptoms.  It started and has never quit. Any help/advice as to where to go next will be appreciated.
Connie

Answer
Connie,
It sounds like you serviced most of the items that can cause shimmys and shakes at higher speeds.  Though you may not have mentioned it, be sure your mechanic checks all the suspension components if they haven't already.  Worn ball joints, tie rods, wheel bearings, and coil springs can cause shaking.  If the frame is bent or support members twisted, it can cause shakes.  Bent or twisted sway bars can cause shimmying.

As for the transmission oil, I only know of the specifications for manual transmission.  As long as your mechanic put in the ATF as recommend in your owners manual, you should be fine without any additives unless it's called for.
Good luck!