Maybe tire shops near you do it for free, but not here. Some will not work on them at any price. They hate vacuuming the stuff and say that it clogs the vacuum filter every time. Have you ever done it? I have and it is a pain.
Yes I have done it - I really don't think its a big deal... frankly, I think that removing bead sealant is more of a pain, but even that takes no time at all with an eraser wheel.... Look - the bottom line is that tire work is just dirty work - it is what it is, dirty and messy work... not my favorite but ya just get through it.
I personally would never buy used sensors since you would not know how old the battery is or how much life is left. That is also the reason I wouldn't stock them.
From my research, the sensors are rated for 6+ years with normal driving - which I'm assuming is something around 12k miles a year... when they aren't moved, they go into a deep sleep mode that makes them pretty much last forever... you have to really get them going to turn on... this is why you have to get a few rotations to get them to read on the dash when replaced - they don't randomly turn on. So I don't think you're taking much of a gamble buying used sensors - but even new ones only cost $20 more anyways if you can't stomach the minut risk.
Additionally - when the batteries do die on these modules, they don't just suddenly go dead.. you'll see them occasionally not report a pressure, and they'll come back... and then randomly go away... so you have plenty of warning to order a new one and have it ready so you can get them swapped when you get new tires put on at a shop if you don't want to do it yourself.
I also would never not recheck/rebalance the tire after breaking one down. I get things rebalanced about every 2nd rotation anyway. Balance problems is just another reason not to use tire sealant.
I never said to break the tires down, I said just break the bead where the sensor is and swap it out... you don't need to break the tire down and remove it from the rim to the swap, and you don't need to rebalance if you do that.
I have all my tires road forced balanced when first mounted and I have them done under 10lbs of variance (spec is 15lbs, most of my tires are actually 7lbs or under)... I've tested it myself where you balance them, break the bead, swap sensors, re-inflate them and it makes on difference to the balance. So now I don't even bother balancing them afterwards when doing that sort of work. If you get them road force balanced correctly the first time (where they actually rotate the tire on the rim to get the best balance) its really hard to get them messed up after that... I also mark the tired on the rim before working on them to make sure the tire hasn't been slipping on the rim - I've found this to be common when the shop uses too much lube to get the tire to seat. And that slipping caused a repeat balance issue.
Anyhow YMMV - but I haven't found this sort of stuff to be all that big of a deal.
Also - I don't doubt that the slime could cause some balance issues, but its purely a temporary fix to get you home or to the shop.... arguably, the plugs could also cause balance issues - along with any tire damage that caused the flat in the first place.
So not using slim to save on a $25 or $43 sensor may or may not be a big deal if it can get you on the road safely and quickly... I was just trying to understand why it was such a big deal, but I guess I now know. Thanks.
