How much Tranny oil does a 2005 Buick Rrendezvous hold?

no you must have two lines for each . one is oil and one is transmission fluid, they both have a supply and return line. As for radiator yes use special lines.

you need to look at the tranny cooler located in radiator that's the only way tranny fluid can get out but how its crossing over to motor oil im not sure unless you also have a motor oil cooler in the radiator.and that will cause tranny problems ,don't try to drive till you resolve these issues., my other thought is oil is leaking out back of motor and mixing with leaking tranny fluid, try draining tranny first to see if motor oil is really in tranny.

It is electronic. Could be defective speed sensor in tranny.

usually, it will be printed on the oil filler cap..
if not check your owners manual
could be 10w30 5w30 etc

Is the speedometer working?

If the radiator has tranny fluid mixed in with the coolant, then you have an internal tranny cooler leak. At the one side of the tranny, in the saddle tank, there is a tube. This tube allows hot tranny fluid to enter the rad and be cooled before returning to the transmission. It should be totally isolated and submerged in the coolant tank. Occasionally they can leak, and the two fluids will mix. You will need a new rad to repair the problem. It would also be recommended to have the tranny fluid and the coolant flushed after wards. Oil of any kind does not mix well with coolant, and could cause future damage to the tranny more so than the engine.

wheel bearing need check

star cheap first check ur tranny oil with car on and if the level is good ,do the tranny filter and see if this helps if it doesnt than you may need atranny overhaul

either reset using a tool at autozone its free or go to the dealership

try changing the tranny fluid the transmission is a very vital device on the car and does need to be taken care of ,and if the tranny fluid change does not work you may have bad sprockets within and you may be better off gettin a new one in which is very pricey and yet if you have the money to do so this is what i recommend but yet it really does sound to me that the tranny is out indefinetly.