I wouldn't buy any RS of that era without pictures of the stanchions. Appreciate you'd be selling with a big dose of caveat emptor, but it's not hard to pop them apart and have a quick look.
I've bought Judies that are cosmetically beautiful (even the upper stanchions) and the lowers looked like they'd been in the sea for 10 years and were fit only for the bin.
Even if the elastomers in the SL are toast, they are pretty easily replaced by a future buyer.
If they are in good shape then clean them up and I reckon like has been said already you could aim for £100 easily, and maybe more.