Oh dear not that.

If its second hand a lot of people have siliconed on the high level brake light... that might be a issue in getting it off. To fix the side brake light cluster pop off the cluster and just run expanding foam tape all around the light cluster rim leaving a small weep hole at the bottom, screwfix sell some for about 7 quid a roll.. They were just too tight to do the whole thing and made do with a donut round the wiring hole. Most leaks do not come from either the high level or the brakes. Its the boot seal its design is the issue. Its fairly easy to fix the fault. The fault is that the water running down the gap between the light cluster and the boot seal drags dirt behind the seal, in winter this freezes and distorts the seal, now water can run down to the bottom inside the seal and hey presto into the boot. To fix remove the seal ( you will need to unclip the boot glass strut and the wiring harness for the rear demister, undo the screw to wiggle out the block) Clean out the channel of the seal, it will be full of black crud, refit using silicon and pinch up all the distortions to the plastic channel former with pliers.Belts and braces add an extra section of stick on d seal above the top of the boot seal to deflect water into the brake light, boot channel. Yo can get that on fleabay for a few quid

Clean the PCV valve....odd juddering, poor fuel consumption rough idle...its amazing what pressurising the sump does to a car.

Well this is embarrassing but one of our c1's 57 plate is due its mot..last two years the rear brakes have been passed but a with a slight bind advisory. As the clutch was, so we thought on the way out , high revs to pull away from the line, high biting point, I though bank holiday bored clutch and brakes time. Glad I did the brakes first..the handbrake cable was slightly seized, no a lot but enough to stop the spring backing the brake off all the way. On the rolling road the brakes worked fine but with two up and a slight incline it was enough to mimic a failing clutch. Two handbrake cables and biting point restored, all is well. To check the cable remove the plastic trim round the handbrake..the adjuster at the rear should have even length of hand brake cable showing..if the bar is wonky a cable is probably suspect.

Has the fuel filter been changed...judder at a particular rev point under load is commonly a lack of fueling.