is a merc 350sl 1973 worth anything in poor no mot condition or should I dump it

stick it on e bay spares or repair

Contact a Mercedes Benz club. They may have a member willing to take it off your hands as a parts car or as a restoration project for a few hundred. Just don't expect an immediate answer.

http://www.geocities.com/mb350sl/

I wouldn't just dump it. Even if it's a rusty wreck with a knackered engine & gearbox, there will surely still be some parts on it that someone with a similar car could use. Stick it on Ebay, or contact Mercedes owners club. Somebody will want some of it!