Most likely comparable model to your E11. As to the high resistance, have you checked for leaks? An easy check is to plug an end (a section at a time) and blow in the other end. Should be sealed tight when all holes are covered. If not, you have leaks. I’ll leave it the Tech folks to comment on how to tackle the overhaul.

 

Leaks. It is amazing how similarly different clarinets play when leak free and holes have appropriate venting.
IMO blowing into a closed section of clarinet is a poor test for leaks. It is difficult to detect air slowly leaving the lungs.

However if you close your throat with your tongue, then slowly "squirt" the mouthful of air into the clarinet by moving the tongue, still sealing, forwards. Then it is very easy to detect that air is escaping.
This process is the exact reverse of sucking a fluid up a drinking straw. It is a slow-motion, gentle equivalent to squirting a mouthful of water out at the dentist. (It is a human "magnehelic".)

For some people , it seems to need practice in order to achieve.