Get a cat, preferably a feral female (spay, please). No mice anymore, she will eat them all. Avoid toms unless you LIKE the smell of car urine.....
You may want to test the AntiMarten protection, too, it may have failed. Shocks the you-know-what out of the mice and keeps them off the car.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!