Good sharing azam318. If the inner glass of the foglight is dusty and with some moss forming, you could actually clean it up. Here's what I did to my old pair of foglights:-
1) Mix some very mild dish cleaner (eg. sunlight brand dish cleaner) and pour it into the inner of the foglight thru the socket hole.
2) Cover up the socket hole and give it a shake (yeah, shake it baby). U would notice that this process will remove some dusty/ oily surface.
3) Then rinse the inner part with clean water thoroughly (but not for too long as u may risk removing the reflective chrome surface).
4) Next, put it under hot sun to naturally dry the foglight, inside out.
5) Seal the gap with silicone sealant (one have to be able to take sourish smell during this process). To get best result, use bare finger to smoothen the edge.
6) Let it dry for at least 6 hours before installing the foglight back.
Tip: U should adjust the socket position facing down as this would prevent water from going in thru socket gap.
Goodluck