To get those old derailleurs to work their best, a bit of tweaking/bending the steel cage was often needed. I'd assume that's a skill that is mostly extinct, as modern FD cages come pre-tweaked. If it is in fact a Simplex prestige FD, everything has to be well lubed, including the plunger rod. The cage angle and height have to be set correctly. If all this stuff is done properly, they work fine. I always felt that Prestige derailleurs were unfairly maligned. I liked them better than Allvits, old Shimanos, or even Duopars. They were harder to set up well than Suntour, true.

That said, I would also probably replace it (if it is a plastic prestige), preferably with a vintage Suntour. If after 40 years the plastic hasn't cracked yet, it will soon.

Also, if the chain is getting stuck between the chainrings, it's probably not the derailleur's fault, more likely the chain. Modern chains are thinner than the old ones. AFAIK it's not even possible to buy a "standard" width chain anymore.