They should all have 2 vented Caps as per an AD that applies to pretty much every Light Single Cessna
Yes, BPF is correct. My recollection was foggy. It's Canadian AD 79-10-14 R1, I did not find an FAA equivalent. I recall the AD coming out, and my assisting in changing out caps at the flying club. Our instruction was to replace the unvented cap on the right tank of the 150's and 172's (I suppose the rationale was that the left tank was already vented, and they wanted to save the cost of second caps per plane). When I bought my 150, I changed both caps, just because I inherited two off a wreck, so I did not give it more thought after that.