1. is a broken steel actuator cable. It's a pain as you will have to break in from the inside to get the door open before the part can be replaced.
2. Less common but what I had. It had the same signs. i.e. not opening and hearing the right noises. But mine opened sometimes. Once a day or once a week. So no broken actuator cable. Everything was replaced and still the problem came back. It happened to be a shaved wire under the driver seat (LHD). This resulted in not enough power coming to the actuator to pull the cable in to open the door. RoelBN55 WPT G4 D3 LHD Team Greece. Now on Dutch license.
1984 TD5 90 Camel to be
P101JWK 1997 CT Disco Now in the Dutch Camel Trophy Museum.
2006 D3 Thailand Media Vehicle Stages 1 & 2
2004 D2 Landmark Auto (much missed already!)
Search on disco3.co.uk for this problem. It does happen and could be a pain to fix a think.
Might be this one http://www.disco4.com/forum/topic27461.html?highlight=boot+catch
Lewis