That's funny. I've been using Captain Tolley's creeping crack cure for a fair number of years and I've never heard of Captain Jacks. I am most definately UK based. Its NOT a cure-all as it needs a fairly fine crack to do its stuff and you DONT want spills of it sitting around as it attracts dirt but it has a permanent place on board as it is a great 'quick fix' that will get you through the season till you can fix the leak that was dripping on your bunk / chart table / locker of kit properly without giving up sailing time. Yeah, you may need to add a little more after a couple of months, but that still better than raindrops falling on your face . . .
As to loose cap rails etc., I am not looking forward to dealing with them as realistically, about 50% of our ones need replacement, not just rebedding :-( If anyone has tackled this on an early J. Rodgers boat, I'd appreciate hearing about any surprises and cautions.