Sick RL11 controller help

I have a PDP-11/34a UNIBUS system, and the RL11 controller just died on me. I haven't a spare RL11 to diagnose it with, so I've been toggling in whatever test programs I can find. The RL02 drives I have, the cables and the packs are all verified good by booting and testing them on an 11/53 system. The symptoms are as follows: o No drive will boot. CPU halts. o Using vtserver, I can copy the first 8 blocks from any drive back to the vtserver host, but then fails on block 8 with HNF (Header Not Found) in the CSR. Always block 8 (blocks 0 thru 7 always read fine). o A toggle-in oscillating head positioner test code (from the manuals) seems to audibly indicate the head carriage is moving back-and-forth continuously. o The machine seems otherwise unaffected. I can toggle in and test basic machine functionality for memory, CPU, interrupts, etc. It seems quite certain that I have a RL11 controller that has stopped working properly. Not having any other UNIBUS disk systems or any way to boot XXDP, I can't do any further testing. The machine and disk were working fine, and I was even running diagnostics on it when the failure occured. My question is this: Is such a sector addressing failure at all common enough that someone could suggest replacing one or more components on the RL11 controller before I try to obtain a replacement and chuck this one into the trash? Perhaps someone has a working controller they could sell? Thanks in advance, -scott staylor (at) smedley (dot) mrynet (dot) com