K-5 Sensor temperature overheat and fail

On my recent holiday to Vietnam I took my K-5 which I've had from new (shutter count 15k) with me as well as a K-x I bought here on the forum. The K-5 worked fine in very hot and humid temperatures where it was regularly about 35 to nigh on 40 degrees C. One day that was not incredibly hot I took a shot and the shutter stayed open longer than it should for the given shutter speed. The resulting photo was streaked with varying colours. After a few more shots all I got was multi-coloured bands. Bizarrely, when I switched the camera off, the LCD carried on displaying the number of shots I could still take and the only way to clear the LCD was to removed the battery.

I tried different memory cards and left the camera off for days with the battery out. Thankfully I had the K-x to carry on with which I did for the rest of the holiday. No matter what I tried I could not get the K-5 to take a photo. The camera itself behaved normally until you took a photo, whereupon no pic would be taken at all, with the same overly long exposure.

Once back in the UK, after a couple of months I managed to get the camera to take some photos, but they had a weird cast in horizontal bands. If I did Live View the camera would soon just show vertical coloured bands.

Yesterday, after a leaving the camera for a few more months I got it to take normal shots for the first time since it played up. Today I took it out and managed about 30 pics before it failed with it multi-coloured stripe issue.

Tonight I took a few (they were fine) and then tried it on live view and within a few minutes the red thermometer had appeared and the camera failed. It seems to me that sensor overheats too quickly. In a few minutes the EXIF value was 51c. I am on the latest firmware and have tried different lenses.

Has anyone else had this sort of behaviour? Is it possible that the sensor's ability to keep itself cool could somehow fail? The camera has never been dropped and nothing seems loose.
Sadly from what I see K-5s go for I don't think it's worth repairing.

FWIW on one of our trips we went right near the Pentax Hanoi lens factory. Strange to think that the 16-85 I was using was almost back at its birthplace!

Whatever the reason, it seems it's time to send it in for a repair quote or to replace it?

I have been agonising over what to replace it with. I do a lot of travel so I think the K-1 may be too heavy and valuable too to have on backpacker-type trips to Thailand etc. I fancy the look of the K3ii for my next trip which is going to be NZ and then Thailand. It will be nice having the GPS.

I'd get another low shutter count K5. They take nice pictures and you know how to use them. As you say, a repair would probably be expensive.

I ended up getting a new K3ii. I think I might sell the K-5 for spares or repair. Such a shame as it's mint and I really loved it.