>>(the single LF receiver is mounted somewhere behind the centre console).

I believe that is a RF receiver, not LF. It is only the four TPMS sensors inside the wheels that can receive LF.

>>Are you having issues with your TPMS system?

Yes I am. Changed all four sensors and they are not getting learned for the life of me & a few tyre places. Getting some OBD codes related to two of these initiators malfunctioning. 


C1341 - Left Front Low Frequency Initiator Channel Failure
C1352 - Right Front Low Frequency Initiator Channel Failure

What's annoying is that there's no good reason to bury the check valve inside the spoiler. It could have been fitted where the inline coupler is, in the short length of hose between the car body and the hatch. Somewhere easily accessible.

Does anyone have tips for removing it? I've pulled off the interior trim and taken out all eight bolts that appear to hold it on, but it won't pull off and I don't want to use excessive force to pull it off for fear of breaking it. I suspect there's a gasket or layer of sealing mastic that's holding it on, or there might be some sneaky hidden plastic hooks just waiting to be snapped off.

The rear washer nozzle has stopped working and I suspect it's the check valve under the spoiler, but I need to remove the spoiler to get at it.

Update: I found this document, so it looks like there is double-sided tape holding it on as well as the bolts.

https://static.nhtsa.gov/odi/tsbs/2016/SB-10081509-0699.pdf

Just done that, the only thing TPMS related is

https://partsouq.com/en/catalog/genuine/search?s=tpms&c=Hyundai&ssd=%24*KwHH6svSgZGBpJSYgKee4uWoir2Tg6LBktja_o7WkNDP1qmwjo6chtbJ0LvWjo_6x9ajxpCGjbSI08-AhNe8tqenpLLHnZCc2daW0M_Wu6j57Pq0vcHCx8DDxY6OnJjWydC0wqTEneX9wMPR3teH0cuO5JzZ1oXQz9anvO3mjM3FobOwvsPFmJSIxtaOjKq0lpbA8tKUup6dzMTSj_P9_sPMwcOLq4OC2OLosLy6sbmxurXp7OqmoKG7u7ONrtzRyLWgvrOxxsvA_uP7v8THxsPCwAAAAAAU7EbS%24&vid=915849060&gid=&cid=150355325&q=TMAD281RAEJ044663

Does not look like what I am looking for; clicking on it yields a "page not found".

Thanks

Try shoving your VIN into the webform at http://www.partsouq.com and drill down into the relevant section to find the part number.