I just installed a set of later 124 seats in my 87 300D so the original light gray leather seats are for sale. Includes front headrests, no rear headrests. Also includes the driver armrest of the set I got. Passenger seat includes original non-memory base, driver seat is not on a base but I'm throwing in a memory base from a 92 124. The driver seat is presently in 4 pieces. No heaters.
The leather is in good condition. Typical seat belt scuffing on the left driver bolster and a crack forming on the passenger seat where your left thigh would be. The padding is typical tired. The driver armrest is not as nice as the rest of set. In fact I don't know if it can be cleaned to match.
$180 pick-up only in San Jose, CA but I'd rather swap for a set of 124 Euro velour or other fabric seats in a color that will match the light gray interior of the car, or a set of 6.5x15" steel wheels. I have an extra later style leather rear seat bottom I'll thrown in if you have room.
Sixto
87 300D