One problem related to oil pump has been reported for the 1998 Audi A4. The most recently reported issues are listed below.
Oil pump failed twice, November 17 1999 and December 1, 1999. Hbl, inc of tysons corner, va presumably fixed it first time. Upon recurrence, I have contacted hbl three times by fax, but have not returned my messages. I consider this to be a major failure, as the manufacturer asks fro the car not be driven when the oil pressure sensor is premanently lit.