The broken-bike-seat saga (such as it was) ended happily: I went to the bike shop and bought a new set of screws for the seat.
The guy who helped me said that the screws break all the time, usually for the same reason mine did: Trying to over-tighten them. “That’s why the company charges $20 for them.” He was more scandalized than I was at the cost. I told him I’d had that first screw for 7 years, which works out to less than $3.00 a year, which ain’t bad.
They also suggested I put some grease on the screw before putting it on. “What kind of grease?” I asked. “Grease with a ‘G’,” they said. Hey, what do I know from grease? Turns out there are several different kinds of grease, at my local hardware store, anyway. I went for grease with a “cheap”, mainly because I don’t need a big tub-o-grease. (Insert snarky comment here.)
They also sold me a packet of goo to put on the shaft of the bike seat, which increases friction and thus reduces slippage of the seat, which is the problem I was having which led me to over-tighten the screw in the first place. So I tried it out. It seemed to help, from my first experience. (They also cautioned me not to use it on the screws, which amused me: Yeah, don’t use the friction-enhancing goo as a lubricant. Got it.)
Anyway, all that taken care of, I biked in to work again today. Made good time, too!