We used Comet straight in through the spark plug holes with a little shot of air to distribute onto the walls. Not sure about pouring it in the carb though. OTOH a 5%leakdown rate is pretty good and not indicative of an unsealed motor, besides this procedure isn't going to help the
oil rings.
On a low mile new motor it's possible for
oil to enter through the intake track and not leave any obvious signs on the valves......yet. Not saying that's what the problem is but it should not be discounted. Pull the intake and run your finger into each intake port. If it's oily you found it. If it's not that then that leaves the
oil ring package.
Frank