Notice:
The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.
You might try heating the outer sleeve and try to pull the inner sleeve out when it's warm. Unfortunately, if you apply too much heat, the innner sleeve will also expand. If you can fill the inner sleeve with water and apply heat to the outer sleeve, you might be able to make it work.
Mine did exactly this. First thing I did, because I sail in a salt environment, was to run hot fresh water through it to dissolve any salt crystals to help free it up. Then I used two strap wrenches to twist it in opposite directions whilepulling it open. The strap wrenches are the kind you can get at Sears that use a heavy duty rubber strap, not the chain kind which would just shred it. About ten minutes of work after the hot shower (literally took it into the shower with me) was enough to free it up. I sprayed it down with WD-40 and ran it the entire length up down, constantly tightening & loosening it to try to get the grime out or at least loosened up, then another hot shower to remove most of the WD-40 and grime, then paper towels to get what was left, then I used Sailkote on it once it was clean of the WD-40.
I just used lots of water and patience. Once it was stiff but movable, I dried it with paper towels and let it sit in the sun unlocked for a day. Then I did the WD40 and worked it patiently until free and followed with Sailkote. I always check to be sure they are unlocked before stowing. If it was locked long enough to corrode together then you're probably in the market.
Notice: The advice given on this site is based upon individual or quoted experience, yours may differ. The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.