you are right.
Nothing loss to add extra K or L in front and run the script again, although the odds pretty small thought.
I used to tried to replace some character from my writing key, like "o" to zero, "f" to capital F.....perhaps i should spend much effort to try again and again with the script.
>10
BTC is worth >$7k at current preev rate. If i were you, i'd try everything to get that money back. $7k is not the end of the world, but i'd have to work for a really long time in order to put $7k in my savings account...
You can try to interpolate all letters you're unsure about, generate addresses starting with K or L,.... Maye you'll get lucky

The other option is to offer a 10 or 20% finders fee and let some REALLY, REALLY, REALLY trusted member try to solve your problem. It's certainly something you shouldn't do very lightly, since it'll involve sending this person everything you know (including the written pk). If you take this path, defenately chose somebody who has been around for a long time, did business worth at least 100
BTC on this forum, has a lot of green trust, didn't change his/her password recently, and can sign a message with a really old staked address. Sending over the private key should be a "last resort", but if it's chosing between forfeiting 10
BTC or giving 2
BTC finders fee and recuperating 8
BTC with a reasonable risk, i'd chose the latter.