Personally, I really don't buy into the whole second pass theory. Granted, there is a major artery that goes from you small intestine to the liver, but I'm still not convinced that the second pass theory is really all that valid.
Anyway, regardless of whether the second pass theory is correct or not, there's little reason to limit your oxymetholone use to 4 weeks. There's tons of evidence that says it's not nearly as harsh as all those shitty online profiles say that it is. Hell, even the PDR recommends that you use 100-150mg/day for 8-12 weeks. I've seen studies that prove liver levels won't even rise above the high normal level after 100mg/day for 12 weeks. The stuff is a little rough on the blood pressure, but if you're doin your cardio you should be fine.
I say just go for it bro. If you're having second thoughts, just go to the doc for a full blood panel. That'll tell you if you should be pullin the dosage back or not.
I agree with Tadger that the harm in 17-aa is overrated. All kinds of shit affects liver blood tests, even excercise. I do orals 10 of 14wks during a cycle.
And of course the inject anadrol will effect the liver as do orals-its still 17aa.