theres a way to "revive" an old panel
1: clean everything really well but be careful not to damage the panel.
2: heat the soldered points.
3: check if voltage changed for the better.
4: replace all wiring if it did.
if that didnt work:
bake it under the hot sun for a couple of hours.
if those didnt work:
its dead, jim
i have revived a few using the above method. no harm in trying yourself. there are times when the panel itself is still good but the connection isnt. rotten wiring, undone soldering