Consistency in bowling stroke

This is the sort of thing much better conveyed in person than online, I think, but I'll give it a whirl.

Here are some steps for you to take to build a consistent, reliable stroke, eventually get a hook/curve back and pick up single pin spares.

1. Buy your own ball. It doesn't have to be super fancy or expensive. Something like this is a decent entry-level ball.
2. Get the ball drilled at a local pro-shop. Get it drilled with a finger-tip grip (with grips) and make sure to get it drilled with a thumb hole, because if you want to advance your game, you have to put your damn thumb in the ball. :-)
3. Go Bowling. You're going to be changing your grip and changing your style, so you are not going to be very good right out of the gate. Your goal at this stage is to get comfortable with your footwork, your swing and your release.

Things to keep in mind when you're getting familiar with your new grip / ball:

1. Squeeze the ball, don't grab the ball. Your thumb should be straight when in the hole, rather than slightly bent. Your index and pinky fingers should be very close to your middle fingers.
2. Keep your wrist straight throughout your swing.
3. Approach the line at a slow, and even pace. Swing your arm like a pendulum. As your arm comes down from the apex, it will build up some speed. Your thumb will come out first on your release, you'll want to lift with your fingers and 'shake hands' with the air.

This should give you a nice hook. As you get comfortable with this, it's easily tweaked to enhance the hook to a point where you feel most confident. But, for now, it's baby-steps.

In order to minimize the hook for single pin spares, you will want to spread your index and pinky fingers away from your middle fingers, allow your wrist to bend backwards, follow through 'straight up' (no handshake) and throw directly at your pin.