You can use SikaFlex; probably a good choice for this application. Where are you at with this job? I was in a similar situation when I bought my 41 5 years ago. Lots of expensive work done to the boat but needed some brightwork and going through.
On the issue of rounding up violently; try adding some rake to the mast. If you don't know how to do this I can give you some pointers. I had the same trouble with my 41 and the way I fixed it was by adding rake and bend which moved the center of effort aft. The forestay turnbuckle was almost all the way closed when I started making adjustment and a hanging halyard showed almost no aft rake or bend. When I finished I had almost 2' of combined aft rake/bend to a 55' mast. That's only a couple of degrees angle but it made a huge difference. The boat now sails balanced in almost all wind conditions without a reef unless it is gusting or it is above 25kts.