gearbox oil milky

hello to anyone who may read this, i am a new RD owner,
i have dumped the oil out of gearbox, yamaha 1982 RD250LC , noticed it to be a little milky,
didnt think much of it, replaced oil with castrol MTX gear oil ?????
is that what gear oil i should be using????
noticed oil is turning a milky colour again, Why????????
is this due to water leaking in somewhere from the cooling set up????

if so is there any advice on where to start looking, which seals, where would it be leaking from ??
as this obviously is not a good thing,

any help would be much appreciated

thank you neil

Hi Neilstar,
Castrol MTX (SAE 10W30) is fine for the gearbox - it is what I use on my racebike with no problems at all.

Regarding the milky colour of the oil, I am no expert but that might be an indication of water in the oil, possibly a leaky water o-ring as it passes thru the gearbox. For a better explanation or other possible causes you could try a PM to Sir Al or Hyside - both very knowledgeable and approachable blokes.

cheers, Max

It could be the o ring on the small alloy tube that goes through the crank cases and into the side cover, but it is more likely to be the water pump seal, and some time this seal lets go because there is to much wear in the water pump shaft.