The brand of the bike in that era really has nothing to do with which components you should use if something breaks.

If something needs replacing, check into the Classic & Vintage forum for information on some affordable and durable replacement parts. Most parts are pretty interchangeable, as long as you aren't talking about a valuable bike, then you may want to keep the parts consistent.

As "hinted at" above, you probably don't want to spend the money to put Shimano Dura-Ace or Campagnolo Super Record on the bike, since the bike is not a top end bike, but stranger things have happened.