the biggest two symptoms are puffing out the oil dipstick (aka increased pressure b/c of clog) and cracked/leaky vacuum lines. Its not too tough of a job, probably 5 hours the first time you do it, 2-3 the second time... Make sure you've got the right manifold gasket (if your planning on replacing it, you might not have to) not the felpro one because that one is generic and doesn't quite fit right.

but before you consider doing the replacement for a clogged system do this: on the plastic air inlet hose between the engine and the airbox there is a connection where two hoses attach. Pull undo the hoses and pull the elbow and that piece off the car. Give it a good cleaning and put back. If there's a screen there pitch it. Then check the system again and see if you still have positive pressure (puffing out the oil dipstick tube when hot).

If you do, try AutoRX and see if that'll clean it out. Yeah its like 30 a bottle, but it does clean your engine pretty good. Use synthetic oil from now on too, you can go another few thousand miles between changes which absorbs the cost of the oil. If you still have positive pressure then you've gotta change.

Unless I'm mistaken and someone please correct me, The breather box is just a large box where the oil settles and the vapors return to the inlet to be burned again. You can clean it out, but if you've got worn hoses and such it prolly is better just to replace everything when if you have to do the repairs..

Then again if you've got a split vacuum line you get to do all this anyway...