I split my CVZ-18, but had to support the sides before fitting and glassing in the stringers, transom, and floor. My overlap, gap, or whatever folks call it, the point where the top and bottom meet, was comprised of rotten wood, patches, and 20 lbs of several types of RTV sealant. In my case I felt the need to do it, but some folks do not have these issues present, so they leave the cap on. I own a red 1985 Timi that will require a full resto, I just have not gotten too far yet. It is torn down however, and split. My gel is in horrible shape unlike yours which appears to be fairly intact. Another possible reason may be when split, you now occupy twice as much area, and some folks have limited space to work with. As for your project, tear it all out, I wouldn't trust that patched center main stringer. Regardless of the model, the process is nearly identical, so many of the resto threads on this site are applicable to your project. Looks like you have a good start, keep the faith!