Sometimes they get varnished up over time. See if you can find some BG MOA oil additive at any local New Car Dealership. The service writers can tell you. It's usually used to augment services and won't be on display. Change your oil and add it in and leave it in. It's about the best cleaner/oil conditioner around and is the best shot at cleaning the valve followers the easy way. This stuff and their fuel injector cleaner is about the best available on the market. I'm sure you can also get it online. There is some on Ebay.

3=(PI.98 SWB 2.8TD-TH92.LWB 2.8TD)Red90 SWB.V6/bal,forged pistons,bore/95SR lkr&spr/2 bouncies/(ARB.w/Gorilla 12K winch/new stg gear/stg&sus/CJ side mirr/cust tow rec/01 SR wh w/Mich 265-70-16LTX/Rancho5000's/Candy Apple/rock crawlers/Hellas/KC's