Thanks. Your experience is terrible - I read your original thread. Panasonic is trying to position themselves in the Pro category, up there wtih Nikon and Canon, so the way they have treated you runs counter to that. Are there any consumer watchdogs (newspaper, tv) that you can reach out to? I would also check if there any applicable laws that apply. In the US, many states have consumer protection laws.
I have an extensive Lumix MFT lens collection and not had any issues. If I go with the 70-200 f4, I'd buy a used copy from a dealer (MBP, KEH, Roberts) that offers some sort of warranty. The used prices are about half off of the MSRP.
Based on reviews, the Sigma seems to be the best one. I'll have to physically see them side by side and decide. For me, a smaller size and weight are desirable, but reliability is important.