Having read none of the posts here about installing this filter (stupid me, eh?) I attempted it by merely reading the instructions that came with it. Mistake !! Whoever designed this is truly a sadist.
Mine had never been replaced since 1999, from the looks of it, so that's 130k miles of debris clogging it up.
I used OEM (charcoal, etc) model which came from ebay for $24 incl shipping.
Like others have said here, getting the old one out was not too bad, but those interlocking grooves ............ like ted_tcb said, "the whole process is barbaric and stupid."
After a few hours I gave up trying to get #2 to interlock with #1; besides, by that time they were so mangled that it just would never have happened anyway. (yes, I did do the silicone spray suggested in the instructions, but that only made everything slipprier & harder to handle).
In the end, just to get the damn things in there, I resorted to sawing off the tabs on the top, on two of them (with my little thin-blade band saw) and eliminating the interlocking aspect. (if you leave the tabs on and try installing them without interlocking them, they won't fit inside: too high).
Yes, I know that without interlocking, there's a little space for the dust & pollen to get through, but the alternative would have been to throw the new (mangled) ones away and just do without any filtering. My knuckles were bleeding, my back & neck was sore, and I'd run out of expletives to use against whoever designed this setup.
This set will have to stay in there for the next 130k miles !
(I've done R & R on engines, trannys, & everything else but this was the worst, I think, in terms of frustration.)