I would probe gently with the current owner before bringing your own lawyer in.
Depending on your temperament, I think it makes sense to do a quick consult with a lawyer to get a 15-20 minute consult before approaching the owner.
Assuming OP doesn't have legal expertise, they are essentially trying to debug a problem in a domain they don't understand. Having a domain expert on hand could be a good idea.
I'd just tell the lawyer that you really want to work things out with your partner. The lawyer can certainly tell you how to make the situation adversarial, but they can also tell you how to approach win-win negotiation from a position of strength.
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Depending on your temperament, I think it makes sense to do a quick consult with a lawyer to get a 15-20 minute consult before approaching the owner.
Assuming OP doesn't have legal expertise, they are essentially trying to debug a problem in a domain they don't understand. Having a domain expert on hand could be a good idea.
I'd just tell the lawyer that you really want to work things out with your partner. The lawyer can certainly tell you how to make the situation adversarial, but they can also tell you how to approach win-win negotiation from a position of strength.