I have my transmission clutch and flywheel all out, i thiks its a good idea to change the rear main seal while i have access... how do i do it? lol is it easy?
If you have to ask, buy a Ford service manual and refer to 303-01B-87. According to that, you need to pull the slinger off (using special tool 303-514 and a slidehammer) and then remove the oil seal (using too 303-519 and the slidehammer.) Install the new seal (using tool 303-516) and the slinger (using tool 303-517.)
It may be possible to do this job without these 4 "special tools" but unless it's leaking I wouldn't try.
when i pulled the flywheel off , i noticed that it is wet and dirty n the back of the block, i dont no if its just wet and dirty or oil. i dont no what to do, i was never low or had to add oil so i guess its alright?
If your car doesn't leave a spot at night, then it isn't leaking. As mentioned earlier, if it isn't leaking, don't touch it.
On an interesting side note: I recently learned that the rear mail seal for my 2.3 mustang is the same as the 4.6 through 2002. In fact, from the early 80s to early 2000's, the 2.3, 3.8, 4.6 and 5.0 all used the same seal.