I just did my cooler leak 3 weeks ago. Its a 23mm bolt for the banjo. I had to use the open end of a wrench. That was the only way. Leave the bolt that attaches the cooler assy to the engine loose to get the banjo bolt into place. There is actually 4 o-rings in the cooler assy. I did the top two, then found out the bottom two were the cause of my leak, so I had to go back and do those. I did not use a new washer on the banjo and I have no leaks now. I may have gotten lucky.

I found that a small mirror and a 10mm wrench works the best to get those two nuts off the bottom of the cooler, by leaning over the motor and letting the mirror let you know what you are looking at.

I didn't have much problem with those. I just got home and am contimplating on if I want to finish today or not, all I got left is the banjo, it sounds like it maty be alot easier if I lossen the cooler.I may wait thought cause I don't have plates yet anyway.
Slashdowg I used four cans (1 can,4 times) to find my leaks and I only THINK I got them all.I'm use to V8's but there's Alot of oil moveing around under these hoods.

tackling mine right now. thanks to this thread, only 1/2 hour to remove. the orings were so hard I had to pry them off.

The hardest part was finding a 23mm wrench. Finally ended up at Sears and found a few thousand $ worth of other tools I wanted.:D