New vehicle in exchange?

Hello my box 350 BT has permanent problems with the gearbox, etc. (permanent in the workshop). My pain limit is now slowly reached. Now I got the offer to exchange. I think to make the exchange. Should I upgrade to a 500 he now (payment for vehicle with even better equipment (full) keeps itself in limits with 8,800 € net) or leave it at the 350 BT. Despite the many threads on this topic I am unreliable. I consider the diesel to be fully ausreic The current 500 he engine is an indestructible long-term runner. I drive around 25,000 KM/per year, but could limit the driving performance to 15,000 KM, as I just bought another small box (because of the problems with my car so far), because I can’t keep the engine running faster than I can. I can’t drive more than 500 KM/h. I can’t drive more than 500 KM/h. I can drive more than 25,000 KM/h. G sure to stay mobile). Besides, I just want to buy this one G for a very long time and not to exchange it again after a few years. Apart from that, the 500 he would have to be switchable to gas if the fuel costs went through the ceiling. What would you do? At all exchange or leave it that way if repair works now. And if you swap, upgrade or old proven? Greeting Tom