Leaking Ranchero

As of a few days ago I thought I was noticing the fill on my FX Ranchero dropping. Confirmed last night with a 250bar fill and under 100 bar this morning - so definitely progressing worse - maybe an o-ring just giving up?

I've removed the airtube and filled it separately and will monitor it through the rest of the day to rule that out first. Assuming the airtube is not leaking - I'm looking for some suggestions on where to look next. I'm wondering - where would I start putting some soap liquid to check for a valve leak?
 
After pulling open the airtube I checked the o-ring which acts as the check valve. It seemed a bit stiff and possibly dried out a touch which could explain the leaking. Don't have a replacement handy so I soaked it in some silicone oil to soften it up a bit and re-installed. We'll see how it holds air over night or I'm going to need to dig for a new oring of the right size. 
 
As of a few days ago I thought I was noticing the fill on my FX Ranchero dropping. Confirmed last night with a 250bar fill and under 100 bar this morning - so definitely progressing worse - maybe an o-ring just giving up?

I've removed the airtube and filled it separately and will monitor it through the rest of the day to rule that out first. Assuming the airtube is not leaking - I'm looking for some suggestions on where to look next. I'm wondering - where would I start putting some soap liquid to check for a valve leak?

Good morning, 

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