Rust prevention treatments

There are many treatments - Kurust, Rustoleum and non-branded versions, based upon phosphoric acid, that turn rust into an inert layer. You'd need to be be able to twist and turn the gate about after pouring it in, to coat all of the inside or find a way of spraying it (360° nozzle on the end of a tube, to allow continuous spraying as the nozzle is pulled back from the far end.

Other treatments, such as WaxOyl provide a protective layer (and havbe their own applicators), but don't convert existing rust.

Do you want to paint it, or put some oily stuff in there to stop water getting to the metal?

Traditionally for cars you spray 'cavity wax' through holes, which coats the surfaces and stops moisture attacking the metal. Waxoyl is a popular brand, but there are others.

You can either get it to use with a spray gun (often needs thinning down) or in spray cans (ideally pre-warm to make it flow better). What I've done before is to first spray with WD40-alike to penetrate all the rusty bits and displace any remnant water, then spray cavity wax on top to seal in the oil.

You can also spray paint, but if you can't prep the surfaces inside you don't know if you've got a good key or if it'll flake off internally.

One thing with a tight space though is that if you block the drain holes with wax you might find there's now water trapped inside, which won't help it to exit later. So another way of thinking is to achieve enough airflow that the metal dries out quickly and water never hangs around to rust.

Theo

I've still got some WaxOyl from the 60's when it was needed on my Mini's subframes. Perhaps I should put it on Ebay.

The Waxoyl 360° nozzle was a nail in the end of the tube however it did work quite well.

Ditto. However the applicator is long gone.

Drill both drain and fill holes, let the inside thoroughly dry. Block the holes with bungs, and fill with oil/old oil, then leave to soak in, before draining. Leave the bungs, in the fill holes, remove drain bungs.

That sound like the way to go. I'll look in a motor factor.

I made the drain holes big enough that I'm sure given the weather we have now it will be dry inside. But it won't stay like that! The way the lock is fitted there are 15mm holes on a vertical surface where the catch pokes through.

Thanks all

Andy