You are correct on the common keys. However, there are many other keys that used to be common and I still turn up on older machines. GR200 (old SQ ), ZB3 (old maytag), GR416, GR419, GR8040, etc etc. I have all these old keys after being in the business for close to 40 years. In my area, I still run into these keys and more. I have a great relationship with almost all of the Techs in my area, and a lot of property managers. When one of them gets a call on a commercial washer or dryer, they give out my name.
That being said, if you run into a machine that you do not have a key for, you either have to get one from owner or if it isn't a common key, then you have to drill it out. I'm not bragging, just stating fact, but I am an expert on coin op washers. From the ones you work on to big, 100lb plus machines you see in laundromats. Lots of owners put in different locks that I don't even have a key for. Then, if they don't have key, I drill. I keep a wide variety of locks and parts on my trucks. The Cams on the locks are different for whirlpool, GE, SQ etc.
Number one complaint on coin op machines is the coin slide or drop coin. I could talk for a while on that, but I know from years of experience that apartment tennants never usually get the complaint specific. They know that they put in the money and it didn't work. Could have been trying to put in canadian money (will not work in slides because they have magnet in them to catch and stop them. ) or bent or deformed quarter. Tennants usually always for sure OVERLOAD coin op machines because they want to get most out of their money. They usually get beat into the ground. So, depending on brand, could be clutch (GE or whirlpool), belts wearing, SQ (triangle bearing and seal pretty common), Maytag (used to replace lots of belts because of overloading), etc.
Let us know what you find out. Also, if owner doesn't collect coin box regulary, box will fill and then can't get any more money in. If it happens on a maytag , old one with painted coin box and bolt through lock, good luck. I had one where the owner lost keys. I know what I'm doing, and it took almost 2 hours to free one up last week and install new lock assembly. Maytags have a 5 coin slide on some older models because there is a cage underneath slide. Money gets trapped and you can't get box out. Be ready to pull your hair out. Drilling out coin boxes is a whole dark science, I'm not kidding. I can get any box out of any machine, that's why I get a lot of calls sent to me.
Just a few thoughts. Let us know what you find and if you need any further help or ideas.