Rick I'm sorry but I disagree... the first time one of your locos takes a dive from the table you'll wish the wheels, gears, axles, etc., could be replaced with the turn of a screwdriver. A replaceable gearbox is always better.
Historically Lionels have been reliable because they are geared tall and turn fairly slowly. Before the advent of electronic speed control, many locos had unrealistically high top speeds, and sacrificed a lot of slow-speed performance in trade. Most O-gaugers simply didn't know better. All high-end brass models, American Models S-gauge and HO scale steamers are made with replaceable gearboxes, wheels, and axles. There are plenty of bronze and steel KTM-style gearboxes which have given reliable service since the 1950s and 60s; this design was also used on later-production Williams Crown Edition and Weaver brass locos, with good results.
Gears DO wear from heavy use, lack of lubrication, and especially improper mesh. When the gearbox/motor mount is built into the frame there's no good way to adjust the mesh. We hope it's right from the factory; if it's wrong you'll find out in a couple of years ;-) Then it will be difficult to replace the gear on the driving axle, and unless it's exactly the same size and lead angle as the original, you've got yourself a $1500 shelf queen. I know that Mike R. and company are trying very hard, but compared to the Postwar era, modern production runs are short and parts availability can get spotty. Being able to replace individual parts or the whole gearbox is a much better option than trying to source an exact replacement for the original. It also makes it easier to lower the gear ratio, substitute a steel-tired wheelset (two wheels and bearings already mounted on the axle) for one with rubber tires, correct wheels that are out of gauge, or convert to 2-rail.
Please don't get me started on the K-Line design. The secondary reduction gear isn't a bad thing, but the motor belongs in the firebox where it can be as large as possible. The worm gear should NOT be affixed to the motor shaft, for the same reasons as cited above: when the motor or worm wears out, you will have to source an exact replacement motor with the worm already installed. Also this precludes use of ball thrust bearings, so the thrust load is borne by the motor bearings--not good for longevity!
When MTH started manufacturing HO scale steam locos, they didn't dare try to pitch their 3-rail "toy train" mechanical designs to that crowd. Especially with today's prices, it's time for O gaugers to expect more. Lionel has used separate gearboxes in a few of their high-end locos (JLC series Y-6b, Vision Line CC2, etc.) I'm glad you're content with the current design and there are plenty available for sale. But I would like to see Lionel AND MTH adopt a separate gearbox and two-piece chassis in all of their newly-tooled offerings.
