Bobbins don't get that worn usually? The paint on these are much the same as on Berninas and is on the delicate side. If they have seen lots of use they are bound to have a few signs of wear. If they run and stitch well they are probably worth going for, the internal parts seem to be rather tough and durable. There are a few plastic gears in these, the advatage with them are mostly the double layer cams, few vintage machines have them, at least if you aim for all metal models. They take lare size needles too, so up you can up the size from the standard #18 if you can find any. I sew all kinds of strange stuff sometimes, like plastic lining, carboard, bull denim,... The larger size needles can have an advantage.
I have a two tone beige and tan Supermatic, I like it. If there are lots of cams with the machine it's probably worth the price, but only if you want them. The case can clean up, it can be a bit of a bother because of the crinkle finish, but with the right stuff and soft brush it eventually cleans up. Refinishing should be within doable. My machine cleaned up well with liquid resin type polish (for car paint), but be careful with the crickle finish on the case, it's nearly impossible to buff out the polish in the creases.
A common issue is the friction wheel behind the hand wheel; as you mention it can develop a flat. The rubber can easily be sanded down to even it out, if it's good quality it will last years. I ended up with an aluminium replacement wheel with rubber O-rings, there solutions and options. There have been problems with some of the replacement rubber wheels, they haven't all been as sturdy as the original. The flat spot has always been an issue, remember to release the hand wheel before the machine is stored away.
Make sure you get the right bobbins, they make a difference. I have seen some use class 15, but you will end up with problems with bobbin thread and tension spring. The right bobbins have a groove across the inside of the"hub", it's needed for the bobbin winder to work properly. They are easy to find, but you have to identify the correct type.
Newly serviced machines in good condition often go for a bit more. I payed abouth $40 dollars for my Supermatic, it needed quite a bit of work, replacement pulley, a few additional bobbins, and lots of cleaning. My machine has been a DIY project, but the replacement parts have probably been at least $60 in addition to the purchase. If it's very worn and in need of cosmetic touch ups, I would hesistate a bit. I have several vintage machines by now, and I'm only willing to pay for that special one I'm looking for. I tend to go for bargain machines.
Last edited by Mickey2; 03-31-2019 at 05:21 AM.