Just from your description I knew it's a wet-slug Ta type. These were used in certain spots where fairly high capacitance is needed, with low leakage. When it opened up, there went the CW filter function. The fresh cap seems to show that it can work, but a regular Al electrolytic is not the proper part here. Ideally and officially it should be another wet Ta for best performance.
But, who cares after fifty years? It's not like it will need to run like new, and over a fully specified temperature range. if you really do want or need it to be like new in this respect, the cap should be the original type, which would be very expensive to get new. The next best would be to find used or NOS ones that are still good, and after that would be a bunch of solid Ta caps in parallel. An even better than original, and permanent solution would be 300 uF-worth of plastic caps, but that's physically impractical.
Ed
