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Hi,

I have a small oil leak coming from the filler plug on the gearbox.



It's been very slowly leaking since I changed the gearbox oil to Redline MT-90 about a year ago, but I recall there was evidence of leakage before I changed it.

I think the plug was definitely tight enough (can't get a torque wrench on it).

Can I use a thread sealer on it to stop the leak? If so which brand/type would anyone recommend?

Thanks

Try thread tape if you want to put something around it. Notice that it's a tapered thread, so just tightening it a touch more is probably enough.
If you have access to a couple of drops of liquid thread sealant, clean the oil from the threads before applying the liquid.

Tapered threads should have a sealant or thread tape (straight threaded plugs will have a seal or soft washer).
Any oil resistant thread sealant should do the job. Also Permatex No.3 Aviation Form A Gasket works great on threads, as does the old Stag Jointing Paste.

There's not a crack in the housing around the hole, is there? That can happen when a tapered plug is overtightened

Thanks everyone for your replies.

There doesn't appear to be a crack in the housing by the hole. When I tightened the plug last year I did it as much as I dared.

My plan of action is to top up the gearbox oil and then buy some "Permatex No.3 Aviation Form A Gasket" and see how that goes.

The material in those threads looks like the remains of a liquid thread sealant, that'll be why it didn't leak before your oil change, using the Permatex will seal it as before.

It's been a couple of weeks since I applied the "Permatex No.3 Aviation Form A Gasket" to the threads of the plug and I'm happy to report that the leak has stopped.

As you can see some of it also oozed out and created a nice bead of sealant.

Thank you RS2000 for recommending it.