I could have guessed that you were using 25g. pins. It is really difficult to push oil through those small pins. Try using a 22 or a 23 once just to make sure it's not just the pin size holding you up. Deep tissue massage can help to break up scar tissue. I only bring up the 25 gauge pin issue because I thought that I had scar tissue problems earlier this year, but it turned out that I needed to heat up my gear to get it to go through that small of a pin. I know you're not a newbie, and neither am I. It's easy to jump to the scar tissue conclusion, but now I know I was wrong, and hopefully you are too.
Ever try injecting your lats? They are pretty easy, and they can hold a lotta gear.