Starting issues

Hi guys some help needed please. After recently taking my 97 300tdi auto discovery to KORC pay n play I had some issues starting it. First problem was while I was there I switched off the engine and when I tried to start it I was greeted by the immobiliser light flashing. Cut a long story short tried to solve the problem and couldn't. I could only think that water had got in to the alarm system some where and I wasn't equipped to sort it there so arranged recovery for the following day. When I got there the following morning the damb thing started straight away and ran perfectly all the way home. Once home I checked the green box in the passengers side footwell and there was signs of water getting in. I cleaned everything up with some contact cleaner and a airline put it all back and made it more water tight. Problem solved!! Or so I thought. The next day I went to it key fob worked perfectly turned the ignition fuel pump kicked in but won't crank. All I'm getting is a clicking when I turn the key. Please any advise would be greatly appreciated as how to 1. Diagnose the fault and 2. Fix the problem. Thanks in advance

Clicking is usually lack of amps to starter motor. Its the solenoid clicking in and out. Check the main earth's (a jump lead from battery negative to engine block) if that doesn't help check the positive contacts from battery to starter.

It may be the starter full of crud. You could try flushing with contact cleaner but removing and stripping would be better.

loud clicking or small relay type clicking , if loud remove starter and give it a good clean/blowing with air line, brushes and solenoid

Thanks for you quick response I will have go tomorrow and let you know how I get on. I'm just hoping it isn't anything along the lines of ECU as that will be far beyond my capabilites lol