Composite header seals

A connector port subassembly for a medical device, the connector port subassembly comprising:

• a connector bore arranged within the core subassembly including a proximal end and a distal end formed by one or more core sections having a substantially uniform inner surface;
• one or more connector blocks arranged within the connector bore;
• and
• one or more composite seal rings arranged adjacent to the one or more connector blocks, the one or more composite seal rings comprising a moulded composite of materials having a substantially uniform outer surface configured to engage the substantially uniform inner surface of the one or more core sections, interior ribs having substantially curved apices configured to engage a portion of a lead, and substantially uniform surfaces on opposing sides of the interior ribs parallel with the substantially uniform outer surface of the one or more composite seal rings.