20 years ago (in Feb) I paid £11500 for a brand new 2.0hdi dispatch. I still run it as my only work vehicle and it is going in for annual service and MOT tomorrow. 160k plus on the clock.
From your posts I understand your VW is several years younger than my dispatch and you are having to replace it because it is falling apart with rust. Personally this would not persuade me to part with £40k (which must be at least a whole years profit for you), to buy another one.
Also from reading your posts, your VW has needed significantly more things replaced on it than my 20 year old van. Personally I think VW is over hyped and over priced.
The trouble is that I believe all new diesel engined vans are drama due to Emissions regulations. VW and Mercedes Sprinters have always had rust issues. All rust issues are very visible with local parcel delivery vans. Vans made by Peugeot and Fiat in their Italian factory (Vauxhall now included) are galvanised, but the latest diesel engines seem to have major reliability issues. Added to that, the paint work is very poor. Fiat and Iveco appear to be using the Fiat sourced 2.3 and 3.0 litre lumps. At one time, the Iveco 2.3 litre engine was better than the 2.0 litre PSA engine or the 2.2 Puma engine.