@Julianw ,
Hi and welcome to the forum. Unfortunately you seem to have a shortage of replies to your post. I will try to help.
May I start by correcting a few details.
Your base vehicle is an x244 model Ducato, with 2.8jtd engine. (Your description 2.8dti is general and could also apply to the earlier pre 2000 2.8idTD engine with mechanical injection.) The 2.8jtd is a common rail engine, with electronically controlled injection.
More importantly the gearbox will be the MLGU model with reverse next to first
The problem with your gearbox could be due to linkage cable adjustment. seized parts, or internal to the box. The last possibility could seriously damage your wallet.
Diagnosing gearbox control problems usually requires an assistant to select gears while the linkage is observed. I have not done this on my x244 2.8jtd, due to lack of need, but I have some notes from an earlier vehicle.
You mention a vertical pin or rod. My old notes report that this control rod moves out when moving across the gate to the left, and is fully in when 5th was selected. Moving up and down the gate was by rotating the rod.
This needs checking or correcting for the MLGU box, but I think that the same motions apply.
On the x244 MLGU 5 speed box it means that the control rod is furthest in for 5th, and furthest out for reverse.
I think that your first course of action should be to read
this thread by
@Crossingkeeper and the thread relating to the later x250 linked within it.
It may be that all that is required, is some lubrication. However I could not get enough movement to apply precautionary greasing on my own vehicle, so resorted to PTFE loaded spray, until I have another attempt.
