If you're not going to be putting big miles on it anymore, here's something for you to consider. One pro who, visits here on and off, once posted that he had experience with multiple slipping manual transmissions which lasted quite a long time. So you might consider taking the wait-and-see approach,
I'll throw out one other thing, based on a personal experience of mine. One morning a few years ago while I was driving to work, I thought there was slip in third. So I started 'looking' for the slip, and 'found' it again. Well, it turned out that during this witch hunt, I was slowing down the clutch pedal release. I had altered my natural shifting habits because I was thinking about it and looking for something going wrong. Once I started letting the clutch out as I had always done in the past, everything was fine.
I'm not writing this trying to give you a driving lesson, or suggest that you're shifting wrong. Only sending it for your consideration, because it happened to me, so I know it's possible.