My old Europa went the same way. In my case, a wrinkle had formed in the seat tube - it'd been there for years, so long I just considered it part of the bike. Over the years though, it had started to bend backwards, in the process bending the seat stays. It too was spotted when I took it in for shifting problems though in in my case, it was a bent hanger causing the problems.

If you've got a frame builder nearby, it's certainly worth getting them to have a look at it but get a feel for what it's worth to you first, repairs could get expensive.

It's not hard to straighten a frame, I've done it myself on the kitchen floor using care and Sheldon Brown's article. In the Europa's case, the bent seat tube was a deal breaker unfortunately - I bought that bike new in the 80s and she's been with me ever since.