Mabuchi's "big guy" has the same basic issues with upgrading/modifying as their 16D and 26D motors, but some "extra" issues as well. It has the same poor material for it's end bell, weak magnets, bad can bushing design and end bell design. It also has the added "non-bonus" of having a weird shaft size. The shaft is smaller than 3/32", but isn't an even metric size either. It's difficult to find bushings to fit the shaft, even though there are still "modern" motors from Mabuchi and others that share the weird shaft size. You can get cheap Mabuchi RS36xx motors and salvage the bushings from those, but they are tough to fit the older FT36D can without resizing them...but at least they fit the shaft properly. The rotating "caged" bushing arrangement in the Mabuchi motors is OK when new and tight, but doesn't stay that way for long under use. When the shaft is splined and you remove the arm without being careful, the bushing will come out with the shaft and is impossible to replace, at least in a way where it will function properly.
Then too, finding nice bearings that will fit the shaft well is all-but-impossible. ***Even the period aftermarket bearings that were sold as being "for the FT36D can", were actually 3/32" bore...a loose/sloppy fit and made for a wobbly armature. To make matters worse, they were flimsy, and only marginally "better" than the awful bearings Mabuchi used in their 16D and 26D motors. With a hotter rewound arm, those bearings WILL fail, especially on a can drive motor. I have never found a commercially-available bearing for the Mabuchi 36D shaft that fits properly AND is solid or "precision"...except for one. Some years back, I got some Pitcan motors, or at least motors that look identical to the "Pitcan", and (of course!) took them apart, because they didn't run well, and nothing about them was particularly interesting, except for the beefy-looking bearings. These bearings were not just solid-looking, they were really "industrial" and "precision" in every which way I could figure. I tortured them some, heated them, spun them doing some "eyeball" checking for run-out and slop, and they seemed easily as good as any modern bearing. Looking through my "36D" drawer, I came across what I think is my last example of these bearings, and after installing it in a can, the darned thing is still just as strong, smooth and tight as I had remembered it to be. Here's a couple of shots of the bearing in it's new home:
So, I guess (?) some who are into the old motors and/or curiosities, may not want to ruin an old Pitcan-type motor, but if you have one and aren't too fond of it, there is at least one thing about them worth salvaging before you toss them. Save those bearings. They aren't *just* really excellent quality, they may well be the ONLY good bearing that actually fits the 36D shaft well!