BDisc Brake Banjo Bolt Washer source

[R68GTO]

I'm having trouble getting my banjo bolt joint to seal. Seems it's a common problem due to replacement copper washers are harder than the originals. I first tried to seal mine with the original washers - no luck. Then bought a set of replacements with the same results. I've torqued the bolt up to 35 ft. lbs. and am afraid to go much higher (spec. is 25 ft lbs.) Anyone have a particular source they've used for softer copper washers?