air leaks at nipples on pete front bags

just bought a 90 379 and am going over it fixing cruddy wiring etc, and i have 3 of the 4 air bag for the front end that leak air at what looks like a plastic nipple comming out of the top plate and has brass fittings screwed into it.took it apart and it appears the plastic has a small split ,tried an extra nut to keep it from spreading when the pipe trhread brass is screwed in but still seeps air.so can this be repaired or do i need to replace the whole bag? i cant believe its freakin plastic!! thanks

 

yes a factory front end as far as i can tell, the fitting screw into what looks like a steel insert thats surounded by a plastic that has threads on the outside that a big nut scews down to the top plate. the plastic is split i guess all the way down. if i was to guess someone had over tightened the brass 90 deg. fittings causing a split. i machined some big nuts to stack on the existing one and put some sealer in the hole before putting the fitting back. but they still leak,just slower

 

no, but now you got me wondering. where can i look to decipher the number? the susp has a trailing arm pivoting at the front,the rear of it has like a double shackle type thing .it has 2 maybe 5-7in bags on each side,one fore and one aft of the axle. the bags have peterbilt logos in red on them[faded].it all looks like its been there a long time?