If that Code is correct, the engine was made on 9 June 2000. If it is the original engine, that would suggest the mower was built late in 2000.

Here is the Operator's Manual:
http://bsintek.basco.com/BriggsDocumentDisplay/iorpFNJU0HsjhJvcv4.pdf

Here is the Illustrated Parts List:
http://bsintek.basco.com/BriggsDocumentDisplay/18jsBLXBnfBhU7y.pdf

If the thrust pad wore out or melted, the clutch operating mechanism in the center of the drive shaft may be in need of adjustment. The pad should not be touching the clutch when the clutch is engaged.