A--HA!
Finally, something I can post a reply to!
I had a similar experience with an 11-87 I bought used.
Making sure the shotgun was empty- I tried to put kroil penetrating oil on the tube, from the muzzle-end, let it sit overnight.
Went to wal-mart, bought a factory Remington wrench with the 4-prongs as listed above (good advice). The 2 cool things about the Remington tube wrench:
1. Less than $10.00 each
2. Has a slot for a 3/8-inch ratchet for a little extra torque...
Carefully secured the barrel, and applied smooth even pressure with a small 3/8 ratchet, came right out. FYI- the kroil had penetrated about 3/4 way down the tube on my shotgun overnight (24 hours, actually).
Cleaned and lubed the bare threads, lube each tube after and before each outing (not going to stick due to lack of my trying
)
I'm very happy with the results.
All the best,