A few weeks during a discussion about the MTH NYC Niagara it was mentioned that the Lionel version has a few shortcomings. One being the universal joint between the motor and gearbox is prone to fail. This is one of the items that's been on my round tuit list and I decided to finally try and find a replacement.
After some surfing around I found something that looked like it could work at Stock Drive Products. Website is https://sdp-si.com/eStore and the part number is A 5Z 8MD304.
The Lionel part is 40-43mm long and drilled for a 4mm shaft at each end. The replacement is also made for 4mm shafts but is only 37mm long. SDP had a similar item that is 46mm long but I didn't think it could be shortened and still work. I am now pretty sure it would not fit. The Lionel item has two universal joints while the replacement has only one but given each joint is good for a 45 degree offset angle a single U Joint is all that's needed given its only off by about 5 degrees. List price is only $8.90 but with shipping and handling it cost 24 bucks or about the same if you ordered the Lionel part with shipping. If a few people that were interested got together and ordered a dozen or so you could likely save half that amount.
Here is a pic showing the new part installed. Note the gaps between the ends and the flywheel and gearbox. There is still plenty of shaft length to tighten the screws to.
Here is a pic with the original universal showing the difference in length compared with the replacement.
Note the replacement U joint is nickel plated brass vs plastic of the Lionel part.
Once you figure out how to get the shell off the frame replacing the U joint is fairly easy. 
Pete
