Meth test came back positive - should we ask for lower price?

[Matthew Duke]

Hello everyone - We put in an offer on a duplex - it got accepted. We were very excited to move in - on the last day of our due diligence we performed a meth test and it came back positive. The seller is going to independently test the house to confirm the meth results. If their test comes back positive - which it will. We are trying to figure out what to do. We plan on asking them to have a professional to come in and clean the house so that the meth is gone. BUT - once your house has tested positive for meth - in any FUTURE sale you have to disclose that it was once tested for meth (you don't have to disclose to renters once it is clean - but you do have to disclose when selling the house in the future). Do you think we should ask for any further money off now that we will have to disclose in the future that it was once tested positively for meth? My rationale would be that the meth results will create a stigma and turn away future buyers even though the house is cleaned and fully absent of meth. 

The house price is currently around $350K. So we are thinking of asking for maybe $5-10K more off. But the Seller could easily come back and argue that the house would be cleaned and therefore that is fair and they shouldn't have to take any more off the house. Thoughts? Opinions? All are appreciated!