The items listed above were all easily cured by the nation's expert on Vauxhall Senators (Paul Spence 0850 693141). The Vauxhall main agent was unable to sell me the right sparking plugs and distributor cap for it (as indeed they were for my 24-valve Senator and 1.6 Cavalier).
For servicing and repairing a Senator, I personally DO NOT recommend Vauxhall main agents; and MASTERFIT will not even look at it for exhausts, MOTs, servicing, etc "because it's over 10 years old"! Are they saying they consider 10-year old Vauxhalls to be not worth maintaining, then?
The repairs were a bit expensive, but then the car is high-mileage, it was relatively cheap to buy and is still a better, feather-bed motorway cruiser than all other prestige saloons in which I have ridden, including BMW 7s.
PERFORMANCE - 132MPH, but I have only given it 9 instead of 10 because it is not as fast as my 24-valve 5-speed manual Senator (149MPH).
RELIABILITY - Only 9 out of 10 because I had to call out the RAC when the starter jammed (can happen to any car).
ECONOMY - Not as good as the 24-valver, but not much worse than 1.8 Carltons and 1.6 Cavaliers I have owned.
COMFORT - Luxurious, armchair, relaxing.