glad you found one, they are around just need to track them down
anyway, there will be a small amount of fluid leakage from inside the cylinder when you remove the exsisiting cap, wont be to much but have some rags underneath the cap to soak it up.
no gasket required but be sure to check the sealing o-ring is ok on the replacement item , if in doubt use the ring from your other one, make sure you lube it a little to ease refitting.
tighten it up to correct torque
and you're good to go, maybe wise to check your oil level and top up if required.
hope that helps and good luck with it.
rob