White streaks and milky appearance are an indication that you have water in your gear lube and / or oil seeping from the gearcase. This is a very serious condition which will eventually lead to serious damage.

Water can get into the drive from a bad seal or a bad o'ring. Seals go bad after a few years and need to be replaced. Usually drives are resealed every 5 years, less if you have overheated your engine.

Water can also leak into the drive if the Ujoint Bellows are leaking. The front main seal of the drive is not really designed to hold water out as much as it is to hold oil in. If you develope a water leak into the bellows it can let water into the drive itself.

When water gets in the drive it tends to condensate on the top bearing. That's because drives have an air pocket in the top. The moisture rusts the race and bearing needles. The water also rusts the shaft races and gears. When the drive is then used the rust "pits" the metal surfaces and bits of metal shave off with each revolution. The metal bits add to the process and soon the gears, bearings and shafts fail.

If you find water in the drive... damage may have already happened. Simply changing the drive lube will not fix or stop the damage. Once a bearing, gear or shaft is rusted, it must be replaced.

Removing the top cover from the drive will usually reveal the level of damage. If the top bearing looks PERFECT (no brown water stains, rust, pitting or streaks) you should be OK. If you see brown stains, the hardness of the metal has been ruined. Don't run the drive with a damaged part(s). You might turn an expensive repair into a much more expensive repair.