Technical Gearbox issues

[Allan1942]

Recently my Adria campervan gearbox stuck in 2nd gear. We removed the gearbox with difficulty (by unscrewing the six hex bolts from the flywheel because the clutch shaft is totally seized) and found a broken spring 9645385880 that was protruding from the synchromesh parts preventing changing out of 2nd gear.
I bought a set of 3 of these springs plus 2 similar 9645385980.
I've reassembled the gears on the shaft after a few abortive attempts and I reckon the parts are now orientated in the correct positions. I couldn't find any pictures of the way the springs were fitted but logic suggested the 9645385880 wedge into the "three-legged" gears.
There's a black plastic thing sitting in the casting under the end of the shaft which looks odd. Is this orientated in any specific way or does it just sit in place naturally?
I have the picture of the gears etc from the Forum Nuovo Ducato ePER (https://eper.fiatforum.com/en/Drawings/Detail/F/T/D06/2E/212/15/7/1/SubSubGroup) but this isn't very clear. Is there any advice on reassembling the gears on the shaft and then completing gearbox work? I'd hate to refit the box and find a problem.
I notice there's not much clearance between the lowest gear and the casing. Maybe it'll be OK once everything is reassembled?
Looking at the broken spring I believe it failed due to bad manufacture. I wonder how common this is?
I'm writing this up for future unlucky Ducato owners so any tips for inclusion would be welcomed. https://www.radiomuseum.co.uk/Ducato.html

 

[Communicator]

Recently my Adria campervan gearbox stuck in 2nd gear. We removed the gearbox with difficulty (by unscrewing the six hex bolts from the flywheel because the clutch shaft is totally seized) and found a broken spring 9645385880 that was protruding from the synchromesh parts preventing changing out of 2nd gear.
I bought a set of 3 of these springs plus 2 similar 9645385980.
I've reassembled the gears on the shaft after a few abortive attempts and I reckon the parts are now orientated in the correct positions. I couldn't find any pictures of the way the springs were fitted but logic suggested the 9645385880 wedge into the "three-legged" gears.
There's a black plastic thing sitting in the casting under the end of the shaft which looks odd. Is this orientated in any specific way or does it just sit in place naturally?
I have the picture of the gears etc from the Forum Nuovo Ducato ePER (https://eper.fiatforum.com/en/Drawings/Detail/F/T/D06/2E/212/15/7/1/SubSubGroup) but this isn't very clear. Is there any advice on reassembling the gears on the shaft and then completing gearbox work? I'd hate to refit the box and find a problem.
I notice there's not much clearance between the lowest gear and the casing. Maybe it'll be OK once everything is reassembled?
Looking at the broken spring I believe it failed due to bad manufacture. I wonder how common this is?
I'm writing this up for future unlucky Ducato owners so any tips for inclusion would be welcomed. https://www.radiomuseum.co.uk/Ducato.html

I found a parts diagram on the web a while back. As it may help someone I will attach it here.