1973 dart sport brake booster

I got the same problem with my '71 booster
I wanted to buy a rebuilt one from Harmon Classic Brakes, but shipping and custom/import duties were prohibitive for me
Can be a good solution for you, in USA
Here's the link :
https://www.parts123.com/parts123/y...~S6ND03R8T017613815730b~Z5Z5Z5~Z5Z5Z50001029z