[Al (astral highway)]

GJ: thanks, I hadn't heard of Dowty washers, but I'll look them up.

In terms of cleanliness, I will wash the container with detergent and hot water in a dishwasher - that should do the trick. The probe won't get very hot. The EHT resistors inside will dissipate about 10W maximum into a few hundred mils of oil, for a few seconds at a time. The oil will be hard pushed to heat much above a few degrees above room temperature.

Whatever the case, its expansion could be an issue and I will need to leave a little headroom for that - easier for a few cubic mils of air to increase in pressure rather than the oil having nowhere to expand and directly interacting the sealant.

Craig: bolts with a sealing washer sound like the way to go, but I'll also investigate that very pricey sealant! I know that essentially, any sealant is only as good as the surface it's bonded to at a molecular level, so prep is important!

Cheers both!