Phil all you need for the RNS retro is the unit itself plus a new gateway revision L or newer. Your current gateway is a C revision.You can getaway without a new gateway but you will have to run a modified FW to stop the battery drain.
http://www.mk5golfgti.co.uk/forum/index.php/topic,23779.0.htmlHave a read through this mate Ebay.de is the best place for a new gateway, look for a newer version such as AD or AF. The last letter goes as such A to Z then AA to AF so far. So L is newer than C but AA is newer than L. Hope that makes sense.Yours is a C and you'll need a L or newer to stop the drain.FW (firmware) is the software the RNS runs on. There are modified versions out there to stop battery drain without changing the gateway.
Your old lowline?? Buttons I'm afraid mate, TBH you probably won't sell it.