I would NOT trade.
The seller is sticking you.
He gets rid of an enlarger that needs a lot of work to get running and is thus hard to sell, in exchange for an enlarger that is in operating condition and thus much easier to sell.
And YOU have to spend time and money to get the Durst into operating condition.
He wins, you loose.
I have a Durst L1000. Replacing the missing parts was time consuming and EXPENSIVE. And I have the condenser enlarger, so I don't have to deal with the missing power supply that you have to deal with.
As was mentioned, if you want the Durst, buy it at a very LOW price, because of the work and money you will have to put into it.
You can argue that just replacing the missing power supply will cost a lot of money, which the seller probably already knows.
If you cannot repair the broken parts, you will have to replace them, difficult to find and EXPENSIVE. In your case, shipping will be a major expense.
I can see the rebuild easily taking a year to do, and cost $500 USD or more.