I hear you. But at the same time, Hasselblads are made from pretty rugged stuff for the most part--all the gears, springs, and things that move parts inside are (unlike, say, an RZ67) made of metal. In many cases, if the camera has no obvious malfunctions, just cleaning out the old lubricants and refreshing them is sufficient for it to work good as new.
I myself have learned how to service the backs--I've got something like seven of them, all bought second-hand, and it's really not hard given the information that's available online to open them up, clean out the old gunk inside, and with new lube and maybe a few adjustments, get them working completely fine. I've got my backs, some of which came to me in "well-used" condition, running butter smooth, I fixed the overlapping first & second frame problem on a couple (that's a *really* simple adjustment), and in none of them did I see any wear on gears and other metal parts that would render them on the verge of giving out. (The only thing inside a back I *have* seen with appreciable wear was the infamous nylon stopper in one of them--but you can still get those from Hasselblad and people make 3D printed versions. And of course you do need to replace the light traps occasionally--but those are also being made by eBay sellers, and it's not really hard to make your own.)
If the camera is working fine as-is, you should just keep on using it. I'm not at all in favor of CLAs just for the sake of it. If it's working without any obvious fault but is a bit "rough" or stiff, then often times a CLA/basic service will get it back to where it functions perfectly, no new parts needed. If Hasselblad, or another high-volume service (Odess, Samy's) won't even do a basic service on a 553ELX, it *may* have less to do with the lack of available parts--which is a genuine problem if an actual repair is needed--than it's just in their opinion not worth the time/hassle resulting from the extra complexity of the camera to service. They might have concluded they can make a lot more cash more efficiently by banging out the simpler/faster stuff, of which they've probably got plenty enough work available, and so don't want to "waste" their time on something a bit more complicated.
I don't see any problem in asking Hasselblad--or any other service technician--if they can do a basic maintenance/clean & lube service with the understanding that if major problems are found, there may be nothing they can do for them. You're still not at zero if that does happen: it may not be worth Hasselblad's (or Odess or Samys) time and effort to source the part you need, or fabricate it. But if you at least know what the problem is, you may be able to find *someone* who can get the part for you, or put it in if you source one yourself. Your camera doesn't mean a lot to those folks, but it may to *you*, and so you might not mind buying a donor body, or finding a machinist/3D printer who can make what you need to get it back working properly.