Parking sensor fault - ruins my otherwise perfect love for her...!

Okay, this is annoying me so much I need to write it down.
I love my car, but this recurring fault is enough that I can't fully recommend someone else buying one. In almost 30,000 miles it has only really blighted 2 full weeks and perhaps a dozen or so solo days, but when it is going haywire it really ruins your drive.
With an annoying "beep beep beep" a message flashes up saying ICS unavailable, followed by the loss of the screen to a clean parking sensors message.
I keep my car very clean, sometimes washing it every day.
The fault can last for seconds, minutes or hours.
Sometimes it will occur a dozen or more times in a day, or even 3 times in a mile.
Enough of an infuriating, annoying distraction to keep your attention from the road.
Washing the car spotlessly doesn't help.
Sometimes jetwashing the sensors seems to, sometimes not. A jetwash is an expensive detour of several miles.
Toyota initially shrugged their shoulders.
I then wrote down several sheets of times and dates of each occurrence, and they replaced the radar unit.
This was after 2 full weeks of problems within a month of each other.
Not had many blips since then, until a couple of full days recently.
However, if you are constantly switching back and forth between them working and not, you forget and I nearly crunched a bollard while parking waiting for the beep....
The other issue is occasionally it will flash red on the front bumper sensor (before packing in).
This has had me get out the car in town to make sure a dog or child isn't in front of me.
Now, knowing it is fake, there is the further risk I do drive over someone by ignoring it in future!
Anyone else suffering the same problem?
On a happier note, just back from London - never seen so many Priuses! Though nearly all were Gen 3s, they were surely more numerous than any other model, more so even than Fiestas and Focuses.

 

I heard only the 15", not 17" wheels on the Gen 4 were exempt - are all Gen 3s exempt?
I hope the car can handle being washed, be a bit disappointed if my sponge compromised the Toyota build quality...
We saw more Priuses in the outskirts, but nowhere near the density of central London. What with my vanity plate, I felt like the king of London! Surprised not to see more than 1 or 2 Outlander PHEVs, as they outnumber Priuses in Yorkshire.
I think I saw more Gen 4s in a day in London than in the rest of the country, ever!