Mystery solved. This is why the shocks were stuck...









The elastomers are actually in good condition, they cleaned up like new.
It was hard to disassemble the shocks. First, the 9" tool I ordered from Amazon turned out to be too short. So I had to put one together like in the youtube video, out of a long 5mm hex bit and a 3/8" extension. Harbor Freight unfortunately does not have those, so emergency trip to local HomeDepot, I am out of $35. Second, in the Husky set of hex bits, the 5mm one (of course) had a machining defect: little metal lips were left in the driver hole, so I had to punch them out before I could use it. Third, the bottom screws were really hard to remove. I was afraid I would strip them, but it worked out.

Now, any suggestions on how to clean that white, hardened residue?
Also, I want to replace the 5 mm hex screws, but they may be hard to find here in San Jose...