Had more or less this on my 2003 FL. 2.5 V6. No start and F4 warning on gear indicator on instrument panel. Normally this means a damaged 'box...
Took out, tested & refitted (same) starter motor 3x before seeing the earth/minus/black cable from the battery to the engine block was loose and damaged.
3 euro for a new collet and it is fine ever since. (Imagine a garage... "oo new starter motor required... or gearbox - because of F4 message...")
I have heard that the starter solenoid contact does wear on the 2.5 v6 engines and a repair kit is 12 pounds. Apparently, the starter motor itself is very reliable (nippondenso).
For the DIY people : removing starter motor takes about 20 minutes. Move the cooling hoses out of the way, remove battery AND battery tray. Then a 13mm socket on the 3 retaining bolts.. after it becomes loose, you might think it won't come out past the angle-iron reinforcement of the suspension strut : just gently wiggle it... it will get past...
Once out, open the back casing of the solenoid (3x 10mm bolts) and check the rubber gasket for wear. If there is corrosion (aluminium oxide) evident, you may have a sticky (ie: rusty) solenoid plunger. Check the 2 copper contacts for evidence of excessive wear..
Clean them.
If you did see corrosion; clean and apply vaseline to the plunger body. Not too much or it will end up everywhere in the solenoid housing.
I did the above before realising that the problem was a departed battery cable-terminal, but it was 'no harm' as there was rust inside the solenoid housing.
If you have starter problems, it is worth whipping out the starter to test it. In my case, it became obvious that the starter was fine, but not when built back in (oh joy).
So I went all geeky and measured 12 Ohm resistance between the '- 'terminal of the battery and the engine block with a multimeter. 12 Ohm is a lot when it should be practically 0.... Having seen this, the rest was easy. (New collet/clamp).
Hope the helps someone...
Never give up... your Landy won't anyway.