What was the outcome for you?

I'm in this same identical situation. I did not do a leak down test. All the usual suspects for coolant loss are fine, don't show any failure.

I'm considering reassembling the car and pressure testing from there, hoping that the water pump although it does not look like it failed was the culprit (or gaskets on the plastic tube behind it).

 

I did not find any sign of a leak behind, under or around the water pump or any of the plastic cooling parts hidden under the intake manifold or supercharger. I replaced ALL of the “old design” OEM plastic parts with new because of the brain damage associated with doing the procedure in the future because of (in my opinion) bad engineering design. I also took advantage of the wasted labor by replacing the supercharger coupler to quiet that thing down. After buttoning everything up I found two issues.
First was the cooling line going to the front of the water pump: The plastic nipple that inserts into the WP had worn off to the point it was several cm too short and could not be held by the retainer clip inside the hole (which also was defective) of the WP.
Second: I found a minor leak on the hose to/from reservoir tank. The “O”-ring inside gray plastic connector on the line from the reservoir (part shown) had failed. It leaked just enough to leave the sweet smell of coolant on a daily basis and eventually, in stealthily way, it sucked and dripped coolant that convinced you it was the water pump. Through trial and error I eventually found the issue and bought some generic o rings, replaced the faulty one and smeared a little silicone around the interior of the gray part and a light coat around the o-ring nipple for good measure and as added incentive to hold coolant. I then let everything sit for 24-36hrs to cure. Also, because I no longer feel confident in a design that screams future failure, I then Zip tied every connection within reach for added holding security. A lot like suspenders plus a belt to hold up your pants. Hope this helps you or someone else.
BTW: I also replaced the WP gaskets, O ring to the oil cooler and the plastic insert. I figured in for a penny, in for a dollar.
Good Luck

 

Just a FYI, zip ties inside the engine area will heat up and break soon, might want to re-think that and use a small metal screw clamp.....

 

Thanks for the FYI, I’m aware of that. I do my own maintenance so everything is inspected regularly.