XKR running issue

Hi

My 1999 Xkr is in the local garage for the last month  due to a running issue.

The car has been stored for two years with just monthly start ups to keep engine moving .

It idles okay but splutters when accelerater pressed and can't be driven.

I changed fuel and fuel filter but it was the same .

The garage tried changing spark plugs , found one pump and its loom had burnt out , and 02 sensors needed changing..

All that work and cost and the car is still the same , well up to 2500 revs it's okay , mthen the same.

The garage is saying if the Denso sensors don't have gold in them they won't work ! British parts are saying that's nonsense !

Any help appreciated