Ok, so have been trying to rack my brain what it might be about these wells for police to target them specifically and I noticed there is something unique about them. Along the entire stretch of road from Budens to Praia da Boca do Rio, these are pretty much the only ones I can find where you can access by simply pulling over to the side of the road.
The larger well is a bit trickier to get to with all the overgrowth but not sure how it looked back in 2007. All the other wells in the area require you to go over some wall or enter onto people's property. There is only one other well I can find which is actually on the roadside and this is quite close to Budens. Here:
37.082586,-8.823732
I'm wondering whether CB has confided in someone about what he did with MM's body and this person has now relayed to the police what he remembers. Perhaps they've known all along she was disposed in a well, but were looking for a rough location that matched with what CB had described to the informant.
We heard weeks ago about Portuguese LE being poised to do a well search, everyone assumed it was at the finca but nothing then happened. This is possibly why there's been all the appeals for where his van was seen. Did CB perhaps tell someone something along the lines of simply "pulling over to the side of the road and tossing her down an abandoned well on his way to/from his beach campsite at the time"?
What did he say in the rest of the 2017 bar confession? "I know all about what happened to MM...". I can't imagine that being the end of the conversation.