Powermaster Hissing/part #

[87GNcospg]

i tried a search and there is so much crap relating to these things i could not find what i was looking for. the search engine on here is a little bit screwy too.
i have a refurbished powermaster unit from autozone. i am not sure on the part number. if anyone knows the part # that would be helpful. it was about 184 bucks for the entire unit. i have seen two #s one was 52-9700 and 52-9702. . . .

today my powermaster unit started making a raspy hissing sound. this happens when i press down on the brake pedal. it goes away after a few seconds then comes back once i need the brakes again. i also saw a little bit of fluid on the top portion of the brake pedal where the pin connects it to the powermaster "rod".
is the hissing sound a simple fix? or should i just get a whole new unit?
i want to fix it if its simple for a couple reasons. 1. i cant find my receipt for the powermaster puchase from a couple years ago . 2. its a little bit easier to replace a part on the unit rather than buy a whole new core.

thanks

 

[suicide six]

AutoZone) 52-9702

 

[87GNcospg]

the item is temporarily out of stock at autozone and now its $357. i swore i bought mine for $184. oh well. i can still use my lifetime warranty if they had any in stock.
cardone.com list the item as RR only. . .