OldIHC

Brake booster are very reliable, but if you are getting brake fluid in the vacuum side of the booster, then the Hyd portion is leaking and needs attention. These booster are fairly simple but rebuild kits are not sold to the public. Your best bet is to send it off to a rebuilder.

ok thank you

With that motor upgrade ,I'm wondering what else is in the truck ,trans ,rear diff , can you post pictures ?

On your hydro-vac , go to Irish Mikes site , page 2 ,mt-53 D , K6-KB6 - K7-KB7 and go to file G12.2 and take a look at what that thing looks like inside , like CB 89 says they are fairly simple , there is a diafram in the control valve that you may have in better shape in one of the other trucks . When you get into one of those things they are pretty simple and although they do have all the parts that are shown in the picture , they are not all suspended in mid air , untill you take it apart , and if you are careful , cleaning and new fluids can help alot . I think that they require an amount of neats foot oil in the chamber that helps maintain the seal . You might concider getting a manual , they also have lots of things you will need to know .

If he is getting brake fluid on the vacuum side the problem is in the hyd side, most likely the push rod seal, as I said, rebuild kits are not sold to the public, so "rejuvenating" a hyd seal is unlikely to work or work for long. Replacing the seal is what is needed, and unless you have the parts, how are you going to do that?
If it was a vacuum leak, than neatsfoot oil might help, but not a hyd leak.
I'd compare the booster to the one on the -6 or -8 and exchange the whole booster. While they aren't complex, dis assembly can cause damage if done wrong or stuff is frozen and then you core might not be acceptable.
I just don't see the point of dis assembly (esp dis-assembling two, one of which might be ok if left intact) when no parts are available
I have two, both worked just fine after 75 years, so if one has a leak it is worth trying another..

the diaphragm must have been bad in the booster i replaced it with the one from the kb6 it does seem to work but i need to bleed the brakes yet i intend on changing the rear axle to a 2 speed from the kb8 it has a single speed in it now it has a five speed OD trans im trying to figure out how to post pictures so you can see how it looks you guys have been a lot of help Irish mikes page is a big help thank you all

There is no diaphram in those, there is only a piston and it only has vacuum or atmospheric on either side.

Look on the passenger side of the differencial and by the fill plug there will be some numbers stamped into the case , that can tell you the ratio of the rear end , also on the end of the pinnion shaft, [ if the insides have been changed ] after you take the drave shaft off . I know that for the KB 6's there was a 6.33 , 5.83 and a 5.14 available . The 5.14 being the best for top end .