I always assumed L1 for LTO1 & L3 for LTO3 but I know you can't assume in this game!
We had fun & games when we first started to use LTO3s & tried various methods within barcode rules. Luckily enough, having just checked ours, we still have it set up for our cleaning cartridges. These are the details we used on our rules:
Barcode Tag: CLN
Cleanings: 25
Media Type: 1/2" Cleaning 3 (shows up as
hcart3_clean in barcode rule summary & media type
HC3_CLN in media listing)
Volume Pool: None (greyed out)
Description: Cleaning Tape
Hope this helps.
Regards, Andy