Red stripe under engine cover, hmmm

[boatweight]

Last weekend I was doing my year end prep to put my boat (1996 ps190 LT1) in storage, sad day but it's getting cold here in Idaho, and I noticed a red spray stripe on the inside of my engine cover. I am assuming that the transmission fluid is leaking from the drive shaft seal, spraying in a circular pattern when put in gear, but I cannot find any major leak so this might be happening at higher speeds.

Anyone have experience with changing the seal? Is it a big job that should tackled by a mechanic or a handy guy with tools?

thanks for the help. Lee