Golf Mk4 2003 - just bought a week ago:

1) No problem noticed with locking in first week.

2) Yesterday, person with plug in diagnostic tool noted that it was indicating a fault with the drivers door - and said that if door was behaving OK it probably didn't matter.

3) (Today) Car did not seem to recognise that the driver had entered and was sitting in the seat. The doors all locked automatically after about a minute, the alarm went off and the door switch for unlocking didn't work.

4) There is also an issue with the boot catch (its a hatchback) - the car is inclined to beep and warn that the boot is open as it is being driven. Is this something needing adjustment, or could it be related?

Is this problem familiar to anyone? Looking on Ebay I see "VW Golf Mk4 Front Right/Driver Side Door Lock Control Unit Mechanism (1997-2005)" for about £50. Is this a likely culprit/fix? If so, is fitting straightforward? Does it need to be matched to the key?