I’m in the process of removing the engine from my 1990 GXL for a rebuild, and have everything disconnected except for one oil line coming from the oil cooler, shown in the picture below. I’ve searched the forums for a way to disconnect it and have spent several hours attempting to remove it from the front of the engine. Does anyone know the best way of going about this?

 

I had no problem, but guess others have had problems so here's one I copied from a write up:
using the 21 mm open to hold the fitting in place, disconnect the hose using the 25 mm flare. In my case, I could not get the hose to disconnect from the fitting, so, using the 25 mm (because it has the best grip), I loosened the entire fitting and hose from the front cover.

 

Sometimes the front cover fitting gets rust-bonded to the hose fitting, making removal difficult with the 2 wrenches. Best way to deal with that is soak the fitting/hose end good with PB blaster, and let it marinate for a while and try again. If no joy there, remove the hose from the oil cooler end. Then when the engine is out, you'll be able to get the hose & fitting off the front cover, and put the hose/fitting in a vice to get those two pieces apart.

 

I’ve read from multiple sources to use a 21 and a 25, however my 25 didn’t fit on the nut in my car. I ended up using a crescent wrench for the “25” nut. I did not try using the larger nut to loosen the entire fitting out of fear of breaking the line, but I’ll try that. Thanks for the help.

 

That makes sense, I’ll make sure to soak it. That’s a good idea with the vice as well, I’ll do that if I can’t get it disconnected. Thanks.