Well, I've just booked my 2005 R1200GS in to Jacksons Jersey for its annual service, which they say will be a 'minor service'. It's done 39500 miles and had its 36000m service in 2017, with a standard service plus air filter and brake fluid changed last year.
Estimated cost = £317, which is less than £400+ but still a fair whack.
I've asked for a breakdown of exactly what will be carried out, but I know that labour costs at Jacksons are relatively high, and they are the only authorised BMW dealer on the island - a captive market .