Q1: In that video he shows 4 designs he made. Only 1 is correct with 75 Ohm to ground on the sync input and 470 Ohm on the output. If you are using one without the 470Ohm resistor it might damage your OSSC because the output voltage is too high.
Can you post pictures of the PCB inside the SCART cable?
Using a sync stripper is generally a bad idea unless your equipment needs it.