Timing chain guides and oil light

Hey just a quick question. I just picked up an 05 range rover. It has the BMW 4.4 engine. I bought it knowing the timing chain guides are broken and it's clattering. The truck runs great otherwise. I am going to change them this weekend but my question is after driving it back to my house, about ten minutes. The oil light came on. I am a mechanic and highly experienced in building engines. My guess is that the chain tensioners are over extended due to the plastic being broken off of the guides. This is causing the oil to hemmorage out of the tensioner pistons and causes a drop in pressure. Anyone here who had the timing guide issues also experience the oil light coming on? I really don't want to dig further into this engine than I have to. It has 180,000 miles on it but runs great other than the timing chains. Wondering if the pump is getting weak as well. Thanks!