Bendix AD-9 dump valve seems to get stuck on.

If there is any more than a little oil in the dryer replace your compressor. It's on its way. Easy to do and shouldn't be to expensive.

 

Just replace Airdryer and cartridge, go from there . Its cheaper to replace the whole unit in most cases .

 

That is the same one I have. About $65 replacement.
I know it's not right but this works. Go to Lowes and in the plumbing section get a package of universal O-rings $2.00. Spray a little oil on them before installing

I keep an extra package in the truck.

 

Yeap,I had to do this because air pressure was not building ! Bypass air dryer !

 

That's the spirit. You'll do fine, I'm just saying, if you're going to do this, do it right the 1st time. You have any other questions, you came to the right place. Somebody usually knows something about anything. Just be prepared to get 15 answers about how to do something.

 

I forgot to ask, what engine do you have?

 

It is rather common for thick oil gunk to get stuck in the purge valve preventing it from sealing when it releases.

The oil could be a sign that the compressor is worn out and needs replaced or rebuilt but it can also be a sign that the drier cartridge hasn't been changed in forever. Put the new dryer on and run it a week or so and then investigate.

 

Plugged up air filter will also cause it to pass more oil.