Ahh that'll be because you don't have the dipstick tube bolted up to the manifold properly. The tube rotates and the bottom of the dipstick rubs against the crank web which wears it away.
This happened to me many years ago with a MK3 cortina. I found out the hard way.

Didn't realise it had broken off so topped up the oil. (unbeknown to me nearly 8 litres of oil in the engine intead of the usual 3 and a bit) Dashing to work one morning - oil and smoke everywhere.

Stripped engine only to find aprox 30mm of dipstick lying in the bottom of the sump
Doubt you'll get it out though with a strong magnet you might be able to 'slide' it allong to the drain hole. Might be worth a try before taking the sump off. New gaskets should be available from Ford dealer, local motor factors or Burton power.
HTH BV
