On my coach, gaining access to the breaker isn't as bad as it seems. There are four screws on the top of the power panel. If you remove the top, it is easier to get to the breakers. Circuit breakers can fail over time. Replacing the breaker could be a simple way to check to see if it is the problem or if there is a problem with the DDEC that is causing the breaker to trip. It is doubtful that the existing breaker could be brought back to life.
As always, be careful anytime you are messing with electricity. The safest procedure is to disconnect the battery cables from both the house and chassis battery banks to insure you don't get a nasty surprise.
I suspect you can have Newell ship you out some matching breakers or you might check with a Detroit Diesel Service Center or take a look
here for some similar breakers.