The classic answer is that "it's not based on mileage but condition". At 133k I would generally expect some gas leakage from exhaust valve stems, but a really well-kept engine might not be that worn yet.
Originally posted by 0ddball i dont really understand how valve stems could be subject to gasses being forced through them ?? its gotta get past the valve head first, in which case youve got bigger problems.
I do know how the exhaust valve works! The exhaust cam opens the exhaust valve every other revolution. At this point the exhaust gas in the exhaust port is at very high pressure. If the exhaust valve stems are worn, some of this pressure will escape into the cam cover, hence the need for a breather there. The cam cover also acts as an additional oil mist condenser for crank blow-by gases which in turn reduces oil consumption and external oil emission.
but is it really necessary on an 8 valve? and if it is necessary....
can i swap the rocker cover round so that the breather pipe is at the other end? there is of course that bit under the cover thats shaped around the cams but i assume its all symmetrical and wont get in the way of anything?