How long do you plan on keeping the trailer? Is the lighting wiring still in good shape. It might be difficult to find direct matchup for the lights.
I use LEDs exclusivly for my trailers that I build. They really are much better quality and and longer life. I can't ever remember changing out a bad LED. If you can find the correct light and you have no problem with the expense, I encourage the change out if you are going to have the trailer for a long time.
I have found that in many cases it is the wiring that is bad, not the lights. BTW, LED back up lights are stupid expensive.