Hopefully, someone will pick up on this post and be able to offer some advice.
I have three of the first issue of Bachmann Class 66s, 66135, 66610 and 66701. All have been in store in my loft in their original boxes for several years, 15+, until lockdown 1,0 when I thought I would get them out and have a play. As they had been stored I decided to give them a run in on the layout. I was very disappointed that they all ran jerkily in both directions. As a start I sent 66135 to Bachmann for service and on its return it ran just as badly so it went back again. This time they fitted a new motor which improved the running somewhat although I am not 100% happy with it. After some research on the interweb thingy I came across Peter Dixon's Torridon Road YouTube channel where relays his experience with faulty class 66 motors. I ordered two new motors and four drive shafts from Bachmann service. Today I fitted a motor and two drive shafts to 66701. It made no difference at all. So what is the answer? I like the locos and as they only cost £69 each at the time I am reluctant to spend much more money on getting them to run correctly. I have removed the bogies and rotated the wheels by twisting the drive shaft in my fingers and I can't feel any resistance. There is plenty of oil on the worm. Perhaps over lubrication is the answer. Should I strip the bogies completely, clean and re oil?
Any advice will be gratefully received.