Not sure what "dust cap" you're referring to but...
The accordion looking deals on the end of the rack housing are called bellows, they are just there to prevent dirt and debris from getting to the real seals.
If you knew what you're doing and have the correct tools it can be done at home.
I can tell by your questions you don't know enough to re-seal at home, and you wont have the tools.
I have re-sealed, installed re-mans, and installed new....all depends on how much you want to spend.
do you want to pay for a re-seal and hope the rack housing is still good.
or if you buy a re-man how much of a gambler that you will get a good one the first try....but can be done at home.
Or buy new and install at home.
An alignment will be needed when done.