My perspex (AKA lexan, acrylic, polymethylmethacrilate) portlights
are fitted directly to the fibreglass hull with screws and sealant.
The boat is twenty years old now and they have started to let the rain
in.

The sealant seems to be good but the screws are all a little loose.
There is a screw on the outside with a nylon washer and a tubular nut
on the inside. There doesn't appear to be any sealant on the screw
other than that which has oozed through from between the perspex and
the hull.

My question is this: Should I just replace the nylon washers when
retightening the screws or should I use some sort of sealant under the
heads. If so what type of sealant bearing in mind that I may have to
dismantle it at some time in the future?

Regards,
Russell
'Octopussy', Jeanneau Attalia