do i have a brake issue, leak on spider?

Doing front axle PM on a M936A1, and found the following "little" bit of oil on the back of the brake pad, seems to be coming from the brake cylinder. no fluid on the pads face or any where in the hub area, only this little bit on the back.
I did not think they contained any fluid (or am I wrong here?)? so is this just years of minor leakage from grease/lub breaking down in the brake cylinder or do i have a bigger issue? (couldn't find any past posts on the cylinders for non hydraulic 5 ton brakes)
1st pic shows bottom of cylinder and wetting on spring and pad back
2nd pic is the spider with pads off - you can see the "wet" stain, no real fluid. (the wet oil stain on the diaphragm tube riser is from penetrating oil I added)
3rd pic is the bottom inside of the pad

so just clean it up and reassembly? need new parts? if so a review of the parts places did not turn up much?





just found this part at Oshkosh (brake actuator piston), does it contain fluid? could not find in TM any info other than parts , but this is the part that "looks" like the source of wetting .

Going out on a limb here. Yes grease only in the self adjusting wedge unit mounted to the backing plate. No fluid in the plunger. If the rubber pancake on the brake can leaked air into the shaft it might push grease out the self adjuster wedge thingy and past plunger seal on to the backing plate? Bad pancake? Sorry just trying to keep my donkey covered. Just a bad plunger seal?
Don't know if you have or plan to replace the old rubber but if not it might be a good idea since you are that far and the front does not have the nasty parking spring to deal with. That would also dis prove that the rubber has a small hole and leaking air into the wedge unit. As said maybe just old grease got hot and ran out the old plunger seal.

Floridianson --that's kind of what I though - just thought i'd ask - some of these guys have scary impressive amounts of knowledge and some pertains to these trucks...lol. my pancakes (diaphragms) are good, replaced them just abit ago... and hey I think the front one had failed -so maybe did blow grease etc... into the drum???? will clean and grease the self adjusting piston/wedges if they come out easy enough, have not tried to remove them.

and by the way when I did my pancakes, I did all of them including the spring brakes. read all the threads and videos etc... and really while there is a chance of failure - if done very carefully and as outlined in the TM, I can't see its more dangerous than spring compressors on old cars. as a lot of the threads stated - don't look down the barrel of a loaded gun and don't sit in the kick back zone.... and a 6$ pancake beats a 140$ can in my book (x 4).
thanks

I have solved my issue with a bit more searching on SS - and an old post by Floridianson - 2015 - had this link

...good link.​

ftp://38.106.177.129/gopettibone/for...20no.%204r.pdf

the link is a vendor manual on the spider - tells each part and what it does, and has a section on maintenance of the plungers etc... they only get a light coat of NLGI #1 grease. and what I found inside my plunger is the same thick black "goo" that had run down the back of my brake shoe. so no problem, just will clean up and apply some new NLGI #1 grease - which I don't have... my bearing grease is NLGI#2.

thanks!!!