Hi Peter, this is the one I used. https://www.ebay.co.uk/itm/Black-Universal-Auto-Car-Roof-Radio-AM-FM-Signal-Shark-Fin-Aerial-Antenna-WT/192593664019?hash=item2cd77a1813&enc=AQADAAADAFjVrDbVsZ8oH%2F8PNHtt9VX4%2Fw7FZcmMuqsX8uaFEduVhXvoTouLhcUcY79O78ElPnZzBugTCpGGaisaCDtm%2B%2FrXokaBRTzLwQiuScUAvYJfZ0sBYA8PuGZcYGAXcXG6MNi8CTZiP6Ggeodo3d68agfYV6ZRbrsM94XBU0YxeLRGdhHepskNOCDTxP0XCuAzSvoiYW6r2o%2BF3kOmTmyVTa9XbRYp5IBNAs%2BcCnO9XwMc70yWhB2y7QLYUwFnivdKP%2BwqIfrnnpl7UFEuP0u2oizArHwT8TGBYHKKb3gRWyEQ0lb57l4D5C5UXWGPtM%2Fl5%2F8HKCXbXJXP%2BZ07SvaPQW16vokPcDNeC%2F0WxairwmCFEMOoHo2BvTOYo3JjPTCaHYuftIaIwxpZ0wTXyhwBUHML0uOz746EZHVJTj0jYbqL5VMQpqGTkk87BBZlzSRkmkMzTFPFp%2BLZnFrg75slmjfNv554kekKUbs9SBtRXRYNQw1NM2dt4WZeh3yagrZn%2FBOKMJEeRBL1f%2FsgUVZ%2BWr8mN%2Fwf6wRIueGJIRjhRZN4SZdipQaDPz8K22pLC8Q3rHFDY43o7I3QtmckRhi0WIht%2BnIVIq2xLaAns%2BsVtCF%2Fx8p7lz9vzxDghgvNLVBJYslzgRvgtYUX0M6Fe%2BXfezDvfbVcb3FIBlS0usQERvKnWgsfltoxYx9D%2BZKBio2mYLDfDkCcRQVhuo4OTB4Ak6T0XazwYqSLCZZy1YxBg1f7tKnM5vdqeysndJiJsQZ09OSbrCBL7dj8f9u3qVpqnHsSewTramkZEZ1jvUrz%2FvWkv4F%2Bp2NDSxuK3ToZd0iwVYMCqEK17yWLIFiN0AMGT9eK6jxGeZwYfV9yQGW2Wgp0aXYQIg2GVbds079WQ6YTteqE44i9rA6hiJVFQ9hJyAZlyGU3q%2FU0Pgfc%2BkGbj8tmu%2BCHgs4%2BIoCqQuh2kxko0Sz7AUUtdcGVYUsFl4AKq%2FJqpqeoU4uWI3hT4RkTzmHMH2m8EQSbOPfqwn2An4s%2FOA%3D%3D&checksum=19259366401972ec63dba8a44b67a608b6408fc62f45
It works fine and the chewing has stopped! As a creature removed it originally I'm guessing it just pulls off. I put the original remains back on (after retrieving it from the ground) and it just pushed back in place. The day before I installed the new one I removed the small screws from inside and sealed it (Stixall) then screwed the plate back on. It's all fairly obvious when you see it. The double sided tape they supply is naff so I bought some better stuff. When the old aerial comes off there's a piece of plastic inside the wire to keep it upright, that just pulls out. The back of the roof is slightly curved so as soon as the shark fin was fixed down I sealed the edges, Stixall again, then cleaned it all up. It sounds a bit amateurish but it looks very neat and tidy. 3 months later and all is good. Also worth mentioning, I used a hair dyer to warm the new one up as it was being fixed, just to help the adhesive as it was very cold.
And I've no idea why the eBay link is sooo long!