Volvo Penta 200x fuel leak from injector

My Volvo 2002(1991, total hours might be 500h or less) started to leak fuel from one of the injectors after removing the injector and installing a new nozzle. The nozzle was replaced for a preventive maintenance recommended by the mechanic who had worked on my Volvo from the beginning. He and another Volvo distributer mechanic recommended to replace the injector sleeve. It was quoted costly. I asked another shop to check it for a second opinion. He suspects the injector itself is leaking from holder at the bottom nut and recommends to replace the whole injector. This costs supposedly much less. I have searched the topic in the internet but have not found the second scenario. Does anyone agree one of the two scenarios?

I have only had a couple bad injector tubes and they all leaked anti freeze.
I would make the first mechanic pull the injector and have it tested. You can have it pop tested for little money.
They pump it up to pressure until it pops, it should leak before it gets up to pop pressure. Ask him if he rebuilt the injector or if he sent it out to a
fuel injection pump , injector rebuild shop. I think who ever put the new nozzle in made a mistake somewhere.

They think it is leaking at number 9 ?

The third mechanic suspected fuel was leaking between 2 and 9. He suggested to test the injector first on the nozzle tester and we did it on Monday. We easily observed fuel along the thread at the top of the nut 2. He removed the nut, cleaned the thread and the inside, and mounted it back after the leak from the thread was confirmed to stop. I went out and ran the engine for one hour or so. So far no leaking.

Take #3's bill to #1