I think it is going to depend on what is wrong with the GP Relays. You will need to look inside and see if the Contact Points are fried/burned up. If so from what I have read there is no replacements.

After that if you can locate any Electical Component that appears Burned; that might be replaced.
After that I simply don't know enough about Electrioncs to test those type of Components.
Unless you are well trained in Electronics I am guessing it is going to be time consuming to the extent that if You could work a couple of Hours overtime you could buy a New Relay.

__________________
84 300D, 82 Volvo 244Gl Diesel