Usually use Sika flex 291. Try some masking tape around the perimeter. Peel offs when mastic is still setting. Make a neat job and saves on the clean up.
Used some good old fasioned linseed oil putty recently, for a simiar job. Easy to use, no mess and about a tenth of the price. Be interested to see if it lasts the pace.
Seelastic, normally found in a caravan shop and I've never known it leak. Remains felxible in the joint forever and only hardens where is squeezes out of the joint.
[/ QUOTE ] or is it Sealastic? Whichever, that is the linseed oil/putty stuff referred to.
It was what I used when I built my boat 30 years ago. Underwater joints as well. No leaks under water although some above have dried out and leaked a bit.
A marine grade silicone sealant should be OK but a polyurethane based adhesive sealant such as Sikaflex 291 will be better if you do not want to remove the fitting again easily. Sika marine products
If you do use Sikaflex, put thin washers under the cleat, so that if you do want to get it off in the future you can get a cheesewire in to cut the sealant