I still have a VHS tape of great Letterman clips from 85-86. I very cautiously watch it from time to time so as not to snap the tape. The best Kenny The Gardener sketch was when he came out and said he was going to transform himself into a rock-hard killing machine and free our POWs from Germany haha...and his song was Gentle On My Mind. Letterman was perfect back then, at 12:30 and often quite absurd and bizarre and always hilarious for the true late-night crowd :)
RU-vid-tied You want the Canopus ADVC 110 to convert that tape! You'll need a Firewire input to use it. It makes perfect digital copies of your VHS tapes that you can edit later. See my transfer of James Brown on Letterman in 1982 under the username "Art's Bar and Grill" as a sample.
This is the kinda stuff Dave lost when he moved to CBS and 11:30pm. This show was Dave's Wacky TV Funhouse. The crew would laugh as much or more than the audience!
I always got the sense that Dave was only so self-deprecating because he genuinely wanted a more slick and polished show, which he then later got. But it was this rougher and less mainstream type of humor that we the viewers loved so much about his show.