Which power brake booster can I use

I’ve got a 69 dart

That I put brakes from a 74 Plymouth scamp on. Front and back disc brakes.
This has the lifted power booster

The power booster has a leak. I can hear it.
I either want to replace it or rebuild it.
Or can I use a substitute.

Rock auto doesn’t have the 74 power booster anymore. I can’t find one.
Other places do have the 76 duster booster. Don’t know if it will fit.

Doesn’t matter what goes on there as long as it fits.

Any ideas?

The picture is what I have now