Canon Service for the UK can be found at:
https://www.canon.co.uk/pro/services/maintenance/
They don't seem to be as straight forward as the US Service as to the cost, but from experience I know that in the US it is clearer what you get and what you pay. Look here and scroll down to the "Maintenance Services Offered":
https://www.usa.canon.com/internet/portal/us/home/support/self-help-center/canon-maintenance-service
This is something that I didn't really think about when I purchased the camera, but even with the 7D I rack up a lot of shutter activations. Just checked and at about 5 1/2 years in I have 76,000 on the shutter count and no issues other than the ubiquitous fine dust that gets into and on everything here in China. That includes carrying it with me through brush, marsh reeds, blowing beach sand, -20°C here in NorthEast China, 43° C in Gulf Coast Texas humidity, it has been rained on and baked in the sun and never failed me. I used the service in the US two years ago for my 7D and they checked out the proper operation of everything, updated the firmware and cleaned the sensor and took care of the reason I sent it in which was an annoying amount of dust that had worked its way up into the viewfinder system. As I remember, the service list included a note saying something like, "Inspected and lubricated shutter system as needed". All for the $129 quoted on the website, which included shipping.
These services are for the higher end "professional" bodies. The RF, mirrorless, bodies are new enough that they don't have a listing on service costs for them, but I would expect, given the cost of such, that they will eventually cover them and be similar in cost. Note that many of the mirrorless cameras of any make do have mechanical shutters, so you have the option of using the mechanical shutter to to avoid rolling shutter on fast moving subjects such as BIF or the Electronic shutter only for higher ISO performance and truly silent shutter.
Back to the original issue - For birding you often just can't get close to your subject and the crop sensors give you that added reach to be able to go back home and crop in really close to verify or solidify that bird your just not certain about. As for what brand of camera, you can get great shots with about any of the front runners. I prefer Canon for the the ergonomics, (relatively) easier menus, excellent color science and truly superb glass. No matter what you go with be sure to check on the cost of the glass to go with that body. No matter what brand the top quality glass to support that top quality body is going to be expensive. The standard go to for birding is generally the 100-400mm zoom lenses. Do to the dust issues I fight, I am considering getting a fixed 400mm or fixed 300mm with a 1.4 extender, but that is a special use case.
Canon has discontinued the 7D so you would likely have to go used there, but it is an excellent choice. The 90D is an interesting less expensive option. My brother went with the 90D and it produces wildlife images that I would say are at least as good as my 7D, in some cases, such as higher ISO, better. Not built for as long a service life though - not as well weather sealed and I think the designed shutter count on it is 100,000 whereas my 7D is 200,000.
I am still tempted to tryout the Canon R body. Specs are a little higher than the RP and still affordable compared to the R5 or R6. Also the high ISO performance is reported to be remarkable and they all are reported to give superb results even with the new very affordable 600mm and 800mm f/11 fixed RF mount lenses. Since I do almost exclusively wildlife, I am considering getting an R body and just keeping a 600mm f/11 lens more or less permanently attached. The other option is to wait until the end of the year and see what the cost is like on the promised R7 crop body.
As for the 6D, it is a great camera, but any of the new RF mirrorless look like they would outperform it, so I would probably advise not going that way.
