Low cylinder compression = engine replacement

Hi,
First time poster here, but I appreciate any advice that can be offered. I live in Ireland and last February I imported a Mazda 6 2.2 diesel from the UK (cars are cheaper there). It was from a trade auction house and had a full service history.

It had been running like a dream until a couple of weeks ago, when I was travelling for work and the 'inspect engine' light came on and I brought it to a Mazda dealer, who did the diagnostics and said it was a faulty emissions monitor. He said this was easy and quite cheap to fix but he did not have the part.

So I brought it home and arranged to leave it up to a main dealer nearby. It has been in the shop two days now and first they told me it looked like a problem with the ERG cooler, then said they needed to do a compression test.

Next they came back and said there was low compression in one cylinder and the engine may have to be replaced and they are waiting on a response from Mazda's goodwill section to see if the company will pay for it.

I have two questions:
1) Is it logical that a fault logged as something simple by one dealer could suddenly show up as something else with another? There is now no mention of emissions at all!

2) Is it possible the second dealer is trying to rip me off? I have heard a number of negative stories about them since, including one where they tried to sell damaged wheels to a customer and when caught, tried to touch them up and convince him they were new!
Can dealers fake this kind of data to send to Mazda?

Much obliged for pointers from those in the know.