Spanner size: Oil cooler pipe

I have a small oil leak on my 1998 300tdi 90 so I need to change the O seals on the Waxstat and oil cooler pipe. Can someone please confirm the size of spanner I need to undo/tighten the oil cooler pipe connection (see diagram). One thread said 24mm but this appears to big. I think it is more like a 22mm or 23mm spanner but perhaps one of you guys can confirm for me. I will purchase the spanner tomorrow. Thanks.

15/16 or 24mm iirc

I thought you could leave the oil pipe attached to the adaptor and just remove the adaptor itself by removing the two 10mm (iirc) bolts on either side. The adaptor then comes out so you can change the seal (or stat)?

Thanks. I think I need to replace the O seal in the junction housing of the connecting pipe as well as that appears to be leaking oil in addition. The brand new 24mm spanner I have appears to be a bit loose on the junction housing which appears odd, so that is why I am questioning if 24mm is the right size spanner for the job. It's a difficult area to access to test a proper fit but was considering buying a 23mm spanner as well just in case. 24mm appears to be the quoted size from what everyone is saying.

use a 24mm. It is a bit loose-fitting but you won't round off any nuts.