My Boler's belly band has white caulking at the edges and I noticed that it was starting to get cracks in it. Do I remove all the old caulking before applying the new stuff? Last time I neatly caulked anything was our new tub... and maybe a window here and there... and that was probably 10 years ago!! I remember wetting an old spoon to smooth the caulking but that's all I can recall!
You should always remove the old first. The new won't adhere to the old very well. Also by getting the old off and out, it gives new key and tooth for the new to grab on to. If you have some on the gelcote you can use a small piece of mica to remove it without scratching the finish. Then use denatured alcohol to clean it before applying the new.