Need help. (was Sanding Bridge Tops)

[justpianos@our.net.au]

List, I need your help.
Today I tuned a Young Chang U-121 upright piano, purchased 20-25 years ago.
I found the bass very out of tune, uneven.
Customer tells me her previous tuner had problem with bass, but couldn't 
explain why.
Piano was twice in storage for considerable time, and 2 years ago moved close 
to me, from about 1200 km. away, interstate.
I closely examined piano, and in trying to tighten bridge screws from the 
back I found them to be stripped. I then explained to the customer that I 
thought this to be the problem and would work out a quote for my next visit.
Customer has just emailed to say bass out already.
Can anybody confirm or deny my suspicions here, and advise on a fix for me to 
quote.
My thought: Loosen bass strings off bridge (do  need to loosen all strings to 
prevent plate cracking), replace bass bridge screws with larger size, try 
injecting glue behind bridge, then replace strings, chip-up, and tune.
What say you?
Bruce Browning - The Piano Tuner.