Take new washers before installation and heat them up with a propane torch and let them cool by air.  The copper may be too hard to form an effective seal.  Heat annealing them renders them dead soft.  Its an old trick I learned working on airplanes. 

Never had that issue. Be sure the bolt is not too long. It may be bottoming out before it clamps the washers? 
Otherwise, maybe just not tight enough.

Ah, but maybe the threads in the caliper giving you trouble aren't cut as deep.  If the washer trick doesn't fix it  would thread both bolts into both calipers until they are tight without the lines, then measure the distance from the washer sealing surface to the underside of the bolt head with calipers and compare. 

Well, I picked up a new bolt and some new washers on the way home tonight. Took the old bolt out and the threads didn’t look great, but ran the new one in with my fingers and it felt fine, so I threw the new washers on and torqued the new bolt down to about 29 ft/lbs.  Torqued the rest of them too for good measure.

I cleaned and dried everything when I was done. We”ll see if it is still dry in the morning.

50vert wrote:

On my 03 calipers, I found that the washer fits into a boss on the caliper. Hadta replace the washer once and couldn't stop it weeping.
Compared the washer to the original and found that there was a height difference. The new washer was not sitting high enough to get enough crush on it.

 
When I removed the old bolt and washer last night, I actually noticed the same little recessed area on the caliper and had a similar thought. The old washers appeared to be slightly larger in diameter than the new washers I installed, so I measured them. The diameter of the old washer was .669” and the new one was .625”. I wonder if the larger washer wasn’t sitting down in that little recessed area all the way, allowing some fluid to leak by?