Can you bring it into the workshop? We have a VERY large crimping tool that can be used on tuning gear heads that often works brilliantly to tighten them. Also, the "wha-wha" sound is a wolf tone and we suggest a setup checkup to make sure the bass is functioning properly, and if everything is "good" about the setup, then you may need a wolf-tone-eliminator.
I would first check to see if your strings are wound properly - perhaps the lack of tension could lead one to believe that the pegs are loose.
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