Earlier Vivaro/Trafic/Primastars suffered from rainwater pooling around the injectors. Removing them then becomes problematic and can involve some very expensive machinery and a risk of warping the cylinder head. Later versions (08 onwards perhaps?) have a revised arrangement of trays beneath the windscreen to prevent this.
I think that you are also, perhaps, suffering from the usual issue whereby it’s mostly the disgruntled that can be bothered to post about their experiences (this is true of almost anything). Look around at the number of Vivaros, Trafics, Transits on the road and it statistically inevitable that there will have been a few problems.