All B19,21,23 and B200,230 motors have them. 16 valves don't, nor do any of the new family all-aluminum engines.

I guess this isn't as widely known as I thought................

Typically any of the affected motors is a candidate for these to have hardened if it is over 8 years old. Milage has never seemed to be that much of a factor, just age.

To replace you remove cam belt and then carefully in 1 turn increments loosen the nuts securing the cam bearing caps. Keep these caps in order for place and direction. Remove cam and and then remove buckets keeping them in order and not losing any shims which are on top of buckets. The seals will be on top of valve spring retainers.

When going back to gether you will need to seal the external caps where they set down onto head with a thin sealant and use just a little bit. Oil can "wick" out through the machining grain at this juncture and cause a false cam seal leak. The external caps are both the front and rear on B200/230 and the front only on B19/21/23. Apply a 1/4" inch wide film across a line from side of cam seal insertion area to the sides. Don't apply any near the cam brg area. You will likely see a residue from where this was done before.

To reinstall cam you tighten nuts on cam brgs in one turn increments until cam is pulled down.

If you fail to loosen and tighten the cam bearing caps nuts in stages of 1 turn per nut on each cap, doing each step on every cap before you go back to first cap and start next step, then you risk breaking a cap or stripping a stud or nut. The valve springs will be loading cam as you do this.