I have both stock and enhanced (with wheel wipers) MTL F7's, and ALL of them will run VERY slowly, down to about a Marklin tie distance per second, or something like that. And they'll pull a house!
My 2-y.o. MTL F7A just started getting sluggish, so I ordered a B unit to help it along. And the B unit included something I don't recall seeing in the A unit's case--the care and feeding instructions. So after how many hours of operation I didn't count, I read that the gears need lube every 50 hours. I see a dis-assembly under magnifying glass session in my future. And while I have the shell separated from the chassis, I'll finally get around to applying the glazing.
NOTE: UNLESS MTL HAS CHANGED THE WORM GEAR DRIVES IN THE NEW ASSEMBLIES: be careful when splitting that chassis, even if just enough to get the truck out ! On each end of the work (shaft above the truck with the brass 'screw' on it), each side has a black round bushing and a very small clear washer ! On the side of those black round bushings, with a little rectangular 'tab'. This goes into a pocket in one half of the casting. If this crazy design is still used in the new generation F7's (last ~2-3 years), then be CAREFUL to make sure they are in place or your loco will likely not even move. Or *much* slower.
