First of all, is the toilet working properly? Second, how important is it to you that the seat be a matching rose color? Third, is this a seldom used toilet or one used everyday? Finally, is it important to you to just get by for now or do you want to do the job right and modernize the bathroom? It seems to me to pretty much a matter of your opinion on those questions to do a $20 fix or several hundred $$ for a new toilet. One could easily argue that a 50 year old toilet has lived its life and should be retired. I would warn you that 50 years ago toilets were installed differently than today so some plumbing on the drain will likely be required to install a new one. It's your call.