No,a transmission on a 2005 mercury mountaineer will not fit on a 2000 mercury mountaineer unless you change the oil message on the mountaineer.
Assuming that you are referring to an automatic transmission- the only place to add fluid is through the transmission dipstick tube. Just be sure that your fluid is low before you add, because there may not be a drain plug (some had them, some didn't).
No , a 2000 Mercury Mountaineer is body on frame
According to the 2000 Mercury Mountaineer Owner Guide : ( Yes , DOT 3 brake fluid , meeting Ford specification ESA-M6C25-A )
The Mercury Sable transmission has a fluid capacity of 12 quarts. You can use any SAE certified automatic transmission fluid.
DOT ( 3 ) brake fluid , if that is what you are asking ?
On a 2000 Mercury Cougar : No , only the automatic transaxle ( transmission ) has a dipstick
According to the 2000 Mercury Sable Owner Guide : ( Motorcraft MERCON - V , automatic transmission fluid in both types of automatic transaxle / transmission )
The engine is fuel injected so there is no carburetor on a 2000 Mercury Mountaineer
it uses Mercon V at transmission fluid. both automatic and manual transmission
check brake fluid level.
The Mercury Mountaineer has hydraulic brakes, not air brakes.