HI Gareth
Unfortunately I was not with the car, but son in law, just passed his test, was. It obviously overheated to the extent that the gearbox was affected as he could not change gear until it cooled down. At that point he checked the oil level which was low and put 1l of coolant in. I am guessing but the car is only used at the weekend and he is putting in 1l circa 100-200 miles.
The sealer was not added by myself, I used the car from 88k to 90k miles over 1 year with no problems. He had the car last June and has done about 750 miles. The only difference was that he did some longer motorway journeys where the overheating problem first appeared.
I have attached an image of the report form the garage, there is no mention of a coolant pressure test.
It may be unconnected but I had a 225 roadster and the previous owner had a fault with the oil cooler which contaminated the cooling system, as when I bought is I did a full coolant flush and replacement thermostat/temp switch, but not sure this explains coolant loss.
IMG_5170.HEIC