I've taken down an old ceiling fan for replacement and found the octagonal junction box to be approx 3/4in above the ceiling, it isn't flush with the drywall which the new ceiling fan bracket mount requires.
I've searched everywhere for a 3/4in deep octagonal extension and can't seem to locate one. The shallowest extension I've found is 1 1/2in which is too deep. The building is old and I don't feel comfortable taking down the old junction box because there are many other wires running through it other than hot and neutral that supply the fan.
Is there something I can pick up or buy online that can make up the 3/4in difference? I know I should just use an extension, the problem is I can't find one that is 3/4in deep.