After retiling the shower, fixing the piping, and re-doing the walls and floor, the time came to put our toilet and sink back in (for those wondering, Part 1 & 2 were one weekend, and the walls/floor were another - we were only sans sink/toilet for an evening, and have a spare toilet).
Old rubber seals may prevent leaks while installed, but do not take well to being un-screwed and re-screwed and shimmied around and are prone to cracking and/or disintegrating entirely so you never even know they existed.
After two emergency trips to the hardware store - one of which involved me pretty literally running into the store at 6:59 to beat the 7 pm close time and playing dumb with the guy in the plumbing department so I could get my part - we got the toilet and sink re-installed.
Luckily, all of the emergency parts were inexpensive - just new seals for the toilet tank-to-bowl attachment and a gasket for the sink - and it just took a couple of tried to get everything tightened up properly and level (as appealing as a tilting toilet tank is!).
Next up....more paint!
And what to do about the medicine cabinet? It's original, and had matched the light fixture/outlet - which we swapped out last summer for a normal light and wall outlet (I can't even find a photo online of this thing; I really should have documented it before chucking it).