I'd simply clean the seats in place using the upholstery tool of a carpet shampooer. Give it an extra rinse and hit it twice with Scotchguard after it's dry.

The passenger weighted seat switch for the seat belt chime goes over and drops down near the seat belt assembly to go under the tunnel carpet up to the chime relay. I found that chime a nuisance if I had something sitting on the passenger seat, so put in a toggle switch under the glove box to be able to disable it.

Depending on your market, most 240s had front seat heater grids and most of those will long have packed it in and needed replacement or repairs by now.

The plastic trim cover over the rear seat rail bolt slides straight back, but there's quite a notch over the two side pins, so some effort may be needed to carefully spread it a bit, push it down a bit and pull it straight back over the notch. Main thing is don't try to pry it straight up or you'll break the side fingers.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now