Critical for you to measure the depth of the hole in the end of the master cylinder piston where it fits against the booster body....and the bore diameter of the original master cylinder....
There are two different bore diameters....
1 1/4" which has a rectangular reservoir cap
AC Delco 18M36288
1 1/8" which has a reservoir cap front and back that are round
AC Delco 18M36246
Buy new unless you like having issues...
