Here is the key. Tap the lifter on its edge to remove as much oil as you can and at the same time pump the button with a magnet. It will act as a pump shooting oil out the inlet hole.
Once you think all the oil is out (which it will not be) , the button should move freely (but with no spring) Push the button in all the way and then bang (very hard) the open end of the lifter down flat on a table using a couple of ply of shop towel or something as cushion. Then look at the button. It should be very extended or almost out (if it didn't fall out) Once you see it extended (may take a couple of bangs, and be sure the button is pushed all the way in before you bang the table) then you can easily pull it on out with your pliers.
Release the oil pressure behind the little ball by using a pick to push the ball a little (check its action) and at the same time squeeze the piston together with your fingers and you will get a shot of oil from the balls hole. Then its free and guess what "There is now very nice spring action.
After I cleaned the parts per Bill's post above, reinstalled the piston (very easy, just slide it back in) the button acted as it should with very nice spring.
I am now working my way checking all the lifters.
The problem is the 38mm 16V lifters which are difficult to disassemble for
The 38mm lifters are also extremely expensive.
The 35mm lifters for the 32V engines are easy to disassemble and clean and much cheaper to buy.