If you're not handy with hydraulics, I maybe wouldn't try it. But it's a simple cylinder, with an additional little angled valve and "hat" seal, and the air valve, which usually is fine. Take all the parts out carefully, line them up, put it back the same way after cleaning etc and looking at the condition of the bore.
Classic Alfa ships in like two days to the US with DHL, still cheaper than the competition.
You can also find repro Mini boosters through Moss and others for reasonable $$, as long as they have 3/8" 24 threads for the piping. 10mm thread is almost, not quite, identical.