Problem With RCA TV

I have an RCA Dimensia Model RVM2731 27" TV. I'm having a reoccurrence of a problem I had a few years ago. The picture is curving inwards at the sides...kind of like this: ) (

The curve is worse a some times than at others. Apparently it is fixable - I paid about $150 to get it fixed last time. Before I take it in again I was wondering if anyone had an idea what the problem might be and if it is something easily fixed.

I'm also interested in references to TV Repair in the southern part of metro Denver, Colorado in case I do have to bring it in.

In it's day (about 1990) this was a top of the line TV. It still has a great picture... I'd like to save it.