Nobody sells a gearbox oil change and almost nobody does one. It is two hours and it decides whether second gear still exists at 200,000 km.
Engine oil gets changed religiously. The gearbox, transfer box and both diffs get changed when something starts making a noise, which is roughly forty thousand kilometres too late. None of these are sealed for life, whatever the service schedule implies.
Gear oil does not burn off; it shears. The long molecules that carry load get chopped up, the oil thins, and the film between gear teeth and synchro cones gets thinner with it. You feel it first as a second gear that baulks when cold — the synchro is not failing, it is swimming in oil that has stopped being oil.
The R380 wants a specific manual-transmission fluid, not the EP90 that goes in the axles, and putting axle oil in a gearbox will make the synchros worse rather than better. The transfer box and the diffs take gear oil, and the diffs on a rear LSD want the friction modifier. Check the plate, not the forum.
Undo the filler plug first, always. A drain plug that comes out of a box you cannot then refill turns a two-hour service into a recovery truck.
Drain into something clean and look at it. Glitter is normal on a magnetic plug and means bearing and gear wear in the usual amounts. Chips you can pick up between finger and thumb are not. A smell like burnt toast on transfer-box oil means it has been run hot, which usually means low.
Four drain plugs and an afternoon buy you a gearbox that outlives the car.
Ivan Petrov · Master Technician
Book it into the Ram Parts workshop, or order the parts and do it yourself — either way you get the same advice.
