Fitting a new rear PDC housing

[UrbanFlow]

Hi,
Took my X for a hand car wash the other day thinking it would be treated gentler - but the over-enthusiastic wash monkeys knocked off both of the rear corner parking sensor plastic housings leaving the PDCs just balanced in the holes. I even went back to try and find them but they had washed away into the drains presumably.

Anyway, bought two new ones from the dealer for a few quid (one Left one Right) and went to fit them.

My question is, it looks like I have to disconnect the PDC unit and remove it, fit the housing and refit. Is that right? as I can't seem to get them out far enough forwards.

Any help/advice appreciated.

UF