None are rubber, usually nylon, nor do they roll, but slide. They are often too firm to turn at all when running against a greased channel. Lots of good replacements out there now that weren't a few years ago, even the channels. Some replacements require you to drill out the original mounts and bolt in new. There's also replacement clip on rollers, but have to measure stud to know size and type. They often had 3 clips on the top edge to remove roller. Otherwise, if they are good condition probably leave them alone as complete regulators are expensive and hard to find, repros come and go and are of questionable quality, I haven't checked lately.
