Up until about 1972, the first 2 numbers were the year of production. After that time, you subtract the first 2 digits of the Serial # from 2000, that gives you the new style production year. I believe they went back AGAIN relatively recently to the original numbering system. I guess yours was from 1981. Contact Chas. Jones, 110 sierra Rd., Kerrville Tx for parts. Good Man!