If the oil light comes on when you park on a slope, check the oil level, it might be just low enough that the slope uncovers the low oil sensor in the pan...
I'm not sure what UK Code requires, but here in Ontario, some form of wire protection MUST be installed in every opening a wire passes through into a box...usually a wire clamp of some form is installed as part of the box [usually non-commercial device (Receptacle or Switch) box] or a screw in wire clamp (it's threads are inserted through the knock-out hole then a starnut is screwed onto the threads clamping the wire clamp to the frame of the box)... The Electrical Inspectors tend to get EXTREMELY testy with a person that ails to secure the wires at the box entry in a manner that also prevents the insulation getting cut by the thin metal of the box...and when the Inspector gets Testy with you, not only do they tend to yell at you, they also tend to issue you a nasty Fine for Violating the CEC and tells you to "Pull it all apart and DO IT RIGHT THIS TIME FOR FRAGS SAKE!!!"* 😄😁😆😅😂🤣 * That's a direct quote from an Irritated Inspector that I overheard in a store being renovated that I was shopping in - only half the store was being worked on and the plastic dust barrier was clear so the customers could stand and watch them work if we were curious, that's why I knew it was an Electrical Inspector ripping an Electrician a New Waste Disposal Orifice and he deserved the chewing out...I could see he'd forgotten several conduit starnuts and hadn't grounded/earthed the metallic conduit properly...
I'm at two minds on grommets, yes they will protect the cable from sharp edges if the cable is rubbing against the steel, But I'm also aware that once the switch or socket is fitted there not much chance of cables moving in the back of the box. I've always fitted grommets because that the way I was taught. Not sure if the regs cover it, think its Advisable but if the cable sheath remains intact there not needed. tbh metal boxes not got super sharp edge and you would really need to work at cut the sheath.
They’re definitely a requirement in terms of Regs, particularly going back to metal DBs as well. Plenty of tripping or short-circuit faults I’ve found have been down to lack of grommets in back boxes. You think they’re not moving but over the years slight house movements, decorators loosening, switches being renewed etc and it doesn’t take much to cut through inner insulation…which is often what you find coming through the hole rather than sheath! Makes sense.
