Temporary fix & charging advice

[Colin Wilks]

I think it depends on the size of the hole. The Fernox sealant says it will need some reinforcement if there's much of a gap. Given you say you may not be able to clean right up to the leak point because of access, I'd go with Hedd's suggestion and clart it up with silicone, although I find when using it that it has a nasty habit of sticking to absolutely everything except the bit you want it to.