Mike I think that this Wix filter will work. You can verify on their website I believe. I have a gl7000 and have bought filters at NAPA, autozone, etc. but have always had the luxury of bringing an old one with me to compare. Walmart Fram's would probably be the cheapest if you could match it up correctly.
Thats what I m saying the threaded portion is probably the same 1" but it may be the length of the filter that is maker specific. He can get a cross referenced part number from NAPA, but it is better to look on EBay and see what is available.