Mk 5 1995 Rear door lock mechanism

[Newton57]

Just become owner of high top conversion motorhome. Rear door lock sad - not sure where to begin. Help please! Central locking mechanism disconnected so guess useless. Need a manual alternative as not securing top of drivers side rear door and lock not operating door to open. Need to use interior handle then go outside to open. This too now keeps failing. Unsure where to begin and failed to source diagram and parts. Based in Notts / Derbys so would like advice and maybe assistance to deal with the challenges. Even considering security padlock? Need easy access to get at gas bottles, toilet cassette etc. so quite important dealt with asap. Thanks.