DIY immobilizer, engine additives, head rests?
 

three for the price of one:

1. i would like to fit some sort of DIY immobilizer to my 200T W123, but can't afford an alarm. i was thinking of something like a hidden switch in the cabin disconnecting the fuel pump. has anyone ever done anything like this and what would you suggest?

2. i have just bought the car and i think the oil was last changed just before the Battle of Hastings, it was black, thick and horrible. i was wondering if any engine additives that claim to coat the cylinders are any good, and advisable or not? if so which brand ro type?

3. the car is fitted with headrests on the rear seats, this unfortunately means i can't fold the back of the seat down flat, the headrests get in the way. i have tried to remove them but can't get them out. are they removable or not. if so how?

thanking you in advance for all your help. jab