So I have contacted Slingshot about getting a quote for installing a master filter. The answer was between $100 - 300...maybe more. Only the Chorus technician could tell me about the costs.
Well Chorus tells me the ISP is suppose to tell me about costs.
Would local electricians do this kind of thing as well?
In that case, I would talk to Slingshot about upgrading to VDSL. I don't know their plans, but it should be the same price as ADSL, and they install a master filter for VDSL, which should rule out any wiring issues.
$20 more than my plan.