Faulty dash? Faulty BSI?Mileage correction?

[Romahomepete]

We have a 2000 Multispace and 2 years ago the dash went Kaput (fairly common I think). The mileometer defaulted to 600000 miles. Because you cannot just fit a s/hand dash because it has to be coded to your vehicle I bought a brand new dash panel. Now everything works except the mileometer which still reads 600000. I am told that when the dash went kaput it sent the mileage setting to the BSI which sent it to the new dash. I have contacted a couple of advertisers of mileage correction and they claim that it can be fixed at a cost of £200+. Since we will keep it forever we are leaving it as it is.