I also have the AL-811H and am quite happy with it. As another post said "it is a great buy".
However, the QC at MFJ just plain stinks in many cases.
The first AL-811 I bought had been dropped hard (pre-packing, box and packing perfect condition, so obviously at the factory) such that one rear corner of the chassis and cabinet was deformed badly...right back to the radio store it went. I have had other MFJ products with joints that had never had solder applied, cold solder joints, etc. In some cases it is like building a kit.
I think it sounds like you have given it a 'fair shot'. You might try one last thing.
!. be sure that it is "deader than a hammer" electrically.
2. take the cover off...be sure it is dead, again.
3. give it a thorough 'exam' - mechanically and electrically.
if no findings, take it back...won't be the first piece of MFJ they got back.
don't give up on it - they are good property.
SOWP, QCWA(50), OOTC, Navy Amateur Radio Club, ex USN Aviation Radio Op. (there was a time when it was ALL CW)