You may have trouble home-rebuilding it. Bendix-Italia does not sell parts thanks to a lawsuit decades ago by someone who bought a then-available repair kit, exceeded his skill level and wrecked his car while testing, then sued the company. Some Pantera vendors do sell a complete replacement.
There is another alternative: an adapted GM booster assembly from Bob Byars at Precision Pro-formance in CA. This booster is a dual-diaphragm type with a slightly larger OD so it gives more boost, has a two-stage aluminum master cylinder with integral keep-alive circuit and is a true bolt-in (being made in the U.S, it does needs 2 short new hydraulic lines with flared ends rather than Euro-style bubble flares). I bought one in 2002 for our '72 and have had zero problems to date. It was also cheaper than the available replacement (for a series-308 Ferrari). Bob warranties his conversion.