Thank you so much for the information! I was for sure able to find the D-17 serial number. That was well hidden!
On the D-19 I was able to find 2 stamped numbers (one above the other) on the lower right side on the rear housing behind the seat. The first number was 4212. The one below it is 7.841. Should I be finding a serial # that starts D19, or did they do this model different? Thanks so much again for your assistance.