Arse:

An exclamation - used frequently by myself when things go wrong, I make a mistake or a body part (mine or the car's) gets damaged.

MOT:

Abbreviation of "Ministry Of Transport" test. A yearly inspection for cars over three (3) years of age, required by law.

N/S:

Shorthand for "Near Side", or in the UK, the passenger side, or left hand side of the car as you are sat in it. Adding an "R" to the end means "Rear", and "F" is Front, e.g., N/S/F is Near Side, Front and N/S/R is Near Side, Rear.

O/S:

As N/S above, but means the Off Side, driver's side or right hand side of the car as you are sat in it.

Sill:

American: "Rocker". Box section on lower sides of car, more or less from front to rear, under doors. Is an important structural feature of most cars as adds strength to body/chassis (and hence, will cause an MOT test failure if corroded/holed).