Even though the rockers are under tension at the spring you can remove the entire assembly at one time by backing out the rocker shaft mount bolts and then just lift the entire assembly off in one unit. Soak the whole assembly in an oil change pan and submerged in water based cleaner like Purple Power or an oil based solvent if you prefer. Periodically scrub with a stiff brush. Once it's resonably clean you'll see more clearly how it comes apart.When you disaasemble the rockers they must be kept in order to ease reassembly. Otherwise you're going to carefully follow a manual to get them right.Based on my experience the inside of the rocker shaft is probably packed with caked oil. I loosened for removal wth a stiff wire then used an engine brush to clean out the bore. Sorry, so long winded, but that's how I've cleaned several of them.

Drew