there are 2 halves to the covers:
192 819 415 C - main cover - 21.62+VAT
192 905 399 A - ecu cover - 5.77+VAT
Check your drain holes arn't blocked, and remove the ECU and check the connections on the plug for cossosion & damp. The plug should be watertight, try smearing a bit of vaseline on the rubber seal before you plug it back in!
I'd also give it a full service, starting with the dizzy cap & rotor arm. Dirt cheap from
http://www.vwspares.co.uk