Here's a repair shop for your address book.
The fuel sendng units on M5's are no longer in production. So replace all 4 and guages is one option. The other is repair. Here is the address of a repair station for the fuel sending units. They are extremely fast turn around. cost is around $120 plus shipping.
Air-Parts of Lock Haven
1084 East Water Street
Lock haven, Pa 17745
email: [email protected]
www.airpartsoflockhaven.com
1-800-443-3117