BMORAN is correct that there has to be a root cause for the sparking. There have been several good suggestions. I have an inherited set of 2353's and they were poor runners from the day I got them in 1968. They mostly sat in storage until 1990 when I had a small layout. They sparked like crazy.
I tried most of the same things BMORAN did. No luck. We moved and I didn't have an operating layout until 2009. I tried again. They still sparked and the rollers got really hot. Cleaning, new grease, cleaning the e-unit -- nothing stopped the sparking. When I disassembled one of the power trucks I discovered that one of the shafts with the gear on it that meshes with the worm gear was slightly bent. I still haven't ordered the part, but will do so when my layout is finished. I'll put on new rollers and replace this part to see if that stops the sparking. Perhaps there is something causing excessive resistance in the drive train or truck bearings that is adding resistance and stressing the motors.
In the meantime, I picked up a set of Williams F3's which effortlessly glide around the layout with 8 aluminum cars in tow. I do miss the growlers and ozone, though.
