I decided to have another try at rejuvenating the standard seats. ESM sell a replacement foam pad for the base that's made from a stiffer foam than the original, so I bought a couple of those, plus I decided to replace the elastic straps in the backrest (I didn't bother with those earlier because they're a lot more hassle to get to than the ones in the base). I took the covers off the passenger seat last night and discovered that the steel frame has broken at one of the joints and needs welding up - it was only being held together by the tension of the base straps.
On Saturday it occurred to me that I really ought to get around to fitting the Riley 1.5 front brake upgrade considering how much I spent on the new cylinders and shoes and everything, so I dug the parts out of storage and found to my surprise that the outside of one of the drums has gone rusty and the paint is all flaking off. These are the drums that I spent a day wire brushing, sanding, rust-killing, applying several coats of high temperature paint, and baking it on. Bizarrely, the unpainted insides of the drums are still rust-free. I'm guessing the black surface attracted condensation and the paint allowed it to soak through to the steel underneath. Wilkinson's Barbecue Paint: not recommended for brake drums.
 The odometer read 70725 miles. I'm noting this for my own reference because I can't remember what the mileage was at the last oil change.