Differences between Pany GX zooms and non GX
The original G14-45 is a metal mount manual zoom lens that is reported to be very good quality. Zoom and focus by ring.
The G14-42 is a plastic mount manual zoom cheaper lens that is approximately the same size. Not as good as the original optically. Zoom and focus by ring.
The New GX14-42 is a metal mount retractable lens that is similar size to the G20mm (Pancake size) and it is power-zoom and power focus (both levers, no focus ring.) Mixed review and like anything new, it is expensive.
Read the review section here: