Honestly, I've never had to check lifters. I've just replaced them when I pulled a motor apart and rebuilt it with a new cam/lifter set. You could check the tension of the internal spring if you had a piece of round rod you could round the end on and stick it down thru each pushrod hole and see if any feel weaker than others. If you're not having any trouble getting them out with that magnet, pull them out one at a time and check em on the bench. You might even be able to disassemble them and clean them internally and then relube them and put them back together and re-install them one at a time so you don't mix them up in their respective bores. It's a pain trying to see how to get them lined up on the magnet to pull them out, but it's do-able. I replaced a cam that way once upon a time, without pulling the intake. Somebody told me I couldn't do it.....lol.