Nned to find the dry weight on my 99 yz 125? - 2003 Yamaha YZ 125

15w40

ATF is normally about 12 weight. You can use it if that weight works for you. I'll let someone else handle the how much part of your question.

Most motorcycle vin numbers follow the same pattern, according to your number, it is an '05.

yz,,,,125,,,, 2,,,,,,,,,g,,,,,,,,,h,,,,,,,,,,,,0,,,,,,,,,0,,,,,,,,,2,,,,,,,,,,,,,,,,5,,,,,,,,,1,,,,,9,,,,,,,
dirt,,,,,mod,,,liquid,,,,,,,,size,,,,,,hp,,,,,check no.,,,,year,,,
street,,,,,,,,,,,,,,air,,,,,,,,,engine

Even though yours doesn't follow exact, it should be close. Some will use codes for the years and other stuff. Look it up on line, you should find it.
my 99 uses x for the year code and my 02 uses 02. Is the YZ a dual sport or dirt?

Suspension Oil "01" as per Yamaha manual

BR9EG NGK

sounds like you may have a base gasket orseal leaking. you should do a leakdown test on motor. buy a manual and it will save you tons of money. a service overhaul manual

You need to ensure for the Carburettor Needle fixed, so that the fuel injected out properly, also if the Crank Gasket should be fitted properly.

www.denniskirk.com-1-800-969-7504orwww.j&pcycle.com-1-800-318-6847. they should have it.

Your bike is water cooled. Some of that water is leaking into the gear box. The cylinder gasket is the likely leak. I would let the shop take a look at it instead of trying to fix it yourself.

But be sure there is not an external source for the water. Do you wash the bike often? Ride the creek bed often? Leave the bike where the lawn sprinkler gets the bike wet? Leave it out in the rain? Change the oil and keep the bike dry. If the problem comes back then go see the dealer.