To fix anything instantly on the car when in the pits (even when your
mechanic says it cannot be fixed), press "F" (refuel) for a second time
when the engine is not running and the handbrake is on.
To be able to race on the test track, open up the !Saloon directory,
and go into the directory "DISC2". Open the directory "!SILVER".
Rename "DATA" as "DATA2" (as a backup for when you want to reverse
the effect). Open the directory "!TESTTRACK" and copy the "DATA"
into "!SILVER". Now run the program and select Silverstone as the
current course. When you race you will in fact be on the test track.