Holes in both cills of MOT candidate

[Tommy21]

Could this occur because the user manual says 'depressions concealed by flaps at the front and rear on the vehicle underbody indicate the points where the jack is to be attached. Fold the flaps outwards to access the jacking points.'?  Experienced car people know that the actual points are inboard of this on the metal seam, but inexperienced jackers may think you remove the flap and attach the jack literally at the depressions on the plastic behind the flap, which will then press on the outer sill itself.

[Migv6 le Frog Fan]

Wet muddy crap gets trapped in there behind the plastic covers and over time eats away at the metal.

[dave the builder]

It is much better NOT to jack a car under the sills in my opinion
I jack the triangle donut plates or front subframe
I've also found using bottle jacks lifts a car strait up better ,
some trolley jacks pull the car up and over because the wheels jam 

[biggriffin]

Cardboard, filler,, lots of black undersill. Old-skool rules.