Multiple seals, internal to a connector block, provide for connecting an implantable medical device and an implanted cable or lead. The forces to engage sealing or releasing the seals are derived from a mechanism so they can be relaxed to permit ease of insertion or withdrawal of a lead, or can be increased to tightly seal against fluid migration, and to provide an electrical insulation between adjacent conductors of the lead and connector block. During implant of the medical device, the lead is inserted and a shaft is rotated with a tool to engage the seals. Later, the seals can be released by rotating the control shaft in the opposite direction to allow extraction of the lead from the connector block. The seals therefore are able to provide improved sealing without increasing the insertion or the extraction forces for the lead.