OK, first apparently I can only edit the body of the post but not the subject header. Let's just forget I mentioned "hopping" since [I]wheel hop[/I] is a thing but something entirely different than to what I'm referring. I have two wheel/tire problems. I'm trying to find how to determine what the problem is (or problems are) and whether it's the same or two different wheels. It's a used car. I know little to nothing of its history; the previous owner claimed to've known nothing about and not noticed a problem. When I first got it there was a throbbing/pulsing/bumping --most noticeable at very slow speeds--that increases/decreases with tire rotation--that I attributed to a possible broken belt, an embedded stone, nail, screw, etc. Visual inspection revealed nothing. Watching someone else drive the car past me, none of the wheels appeared irregular. Later, I found in the car a package of tire plugs with one missing and assumed this might be it. I don't know if this is due to a bad tire or wheel; one of the (alloy) rims may be bent/dented. I know it seems it should be fairly easy to, at least, determine whether it is front or rear, driver or passenger side but, for whatever reason, I've been unable to. [B]Any suggestions on methods to determine which wheel has the problem other than swapping out each, one at a time, with a fifth wheel?[/B] On the car are four 205/50R17. I have a (universal bolt pattern) rim with a 215/45R17. [B]Could this be temporarily used to do the one wheel at a time swap or would this mismatch introduce different problems?[/B] If I took it to a tire shop, would/could they do anything other than using the balancing machine? [B]Would a trip on the balancer determine the culprit, regardless of the cause, wheel or tire, belt etc. or only if the weight is off balance?[/B] Problem two is that more recently, a slow leak has developed. It gets low every few days. I know how to handle this if it's due to the usual causes (valve stem, bead etc.) but would like to first determine whether there's a connection to the first: bent rim or similar. Thanks for any assistance, suggestions, etc.

120k miles or so. in 2014 my left rear caliper seized, tore up the rotor and was a costly repair. Dealer recommended replacing BOTH rear calipers to avoid issues with the one that didn't fail. Last week, loud brake noise and grinding, took back to dealer. Left rear caliper seized again. They actually said it was both that seized, and coincidentally, both were replaced. I expressed my displeasure with the dealer and my anticipation of them contacting the manufacturer, as I don't believe I should be paying for this again. of course, no recalls or TSBs, and they said it's same original equip. caliper. Could another brake component be causing this failure? Thanks!