Solarbird 
hey, there’s a bike chain under all that rust!
(continued from: https://mastodon.murkworks.net/@moira/115069944638186131 )
i’ve put it in denatured alcohol for degreasing and actual cleaning. not sure how long tho’? it’s a lot cleaner already, rust aside.
WHAT’VE WE LEARNED TODAY SOLARBIRD?
don’t put your glass full of evaporust and metal into the ultrasonic
technically learned this yesterday BUT it’s important
LIKE THE XENOMORPH HAS A SECOND SET OF TEETH
THIS THING HAS A SECOND SET OF SPLINES
AND THESE ACT LIKE A FREEWHEEL
holy shit
i also figured out how to get the axle out after only incurring minor and inconsequential damage
however, that just kind of leaves you with a bunch of free bearings and some of them want to go on walkabout so i had to put it back
on the good side the bearings actually look okay? and once i disassembled it as much as i did it suddenly felt better so the bad bearings part is at least _partially_ external components i can try to fix
Oh btw what all this means is:
1) both bike store guy AND i were wrong
2) this CAN be removed from the wheel and replaced, albeit as a set rather than as individual sprockets
3) the lowest two gears are the only ones that show wear but they do show wear so in the unlikely event we get to that point I might actually be able to get a new set of gears _without_ having to replace the wheel
so that's good!
price of tool from eBay, with shipping AND tax: $7.93 because I found a return.
(my LBS don't stock this tool, they have them in shop but not on shelf so)
Trouble@moira that fits the most common "freewheel" as I've been taught. A "cassette" is a higher end product where ratcheting mechanism is separate from the sprockets, and designed to be replaced separately. I'm surprised your bike shop got it wrong. Be ready to use the largest wrench you've got, maybe with a breaker bar. This is the tightest thing on a bike you will ever find. I recommend putting the wheel on the ground when trying to loosen it. (No chain whip; that's for cassettes) Good luck!
@moira I can send pics tomorrow from our bike kitchen if you would like.
@trouble the inner ring of splines was literally not visible due to layers of outer stuff including another set of splines. it doesn’t look like any of the images on park tools’s guides either until you get more layers off. (also they were looking at a photo I’d taken with not enough parts removed yet.)