Freelander 1 Manual gearbox gasket plug

Hey guys. Quick spec; Freelander mk 1, 2006 TD4 Diesel.

My gear box is leaking oil from the lower draining plug. I'm guessing my only choice is to drain completely > replace the O ring > fill back up.

That being said, I've never needed to find/buy an O ring rubber gasket as they usually come with filters and such. So how do I know where and what to buy? Buy a wide selection of rubber plugs from halfords?

Get me? Proper basic bread and butter question. Never had to do this before.

I need to know how to replace an old gasket. Rubber? Copper? Size?

Doesn't have any type of seal on the manual box.

If I were you I'd buy a little tray selection of copper washers, a clean drain tray and an oil transfer hand pump. You can then pull the drain plug, clean/inspect the sealing surface, fit an appropriate copper washer, then pump the lot back in.

Please ensure you crack open the fill plug before starting - that way you know you can refill the box.