Cool to see you are still going on these I use to do a lot of urethane casting for work producing short runs of prototype parts from silicone tools It's hard work but satisfying when you produce the prefect part.
Have you tried using some anti foaming agent in the urethane such as
http://www.bjbenterprises.com/af-4/ It could help lower your failure rate by reducing air bubbles in the urethane before you pour and it also helps it to degas it faster. I have no association with BJB but have just used the product in the past and it does help.
Also if you polish the pins they will pull out of the casting with less resistance or risk of cracking the casting. Keep up the good work cheers