Don't hold me to this being technically quite right, but here's how I think it works:

There are two coils in the solenoid: a high-current one that makes it throw quickly when engaged, and a low-current one that keeps it engaged. There are point contacts that switch between the coils once the high-current throw is complete.

The solenoid arm operates a little ball valve that forces the high-pressure oil circuit into operation, and it takes some current to keep it seated. For some reason I don't understand at all, it takes less force, and less current, for the ball to seat on decceleration.

If the low-current coil has a resistive connection, you'll get the symptoms you describe.

So... 1) clean the points under the rubber boot and plastic cap, 2) reflow the solder on the coil wire connections -- no need to add more solder, just reheat the existing solder to freshen it up.

Also, if you replaced the solenoid, did you adjust the new one? There's a hole in the pivot arm that must align perfectly with a hole in the case casting when the solenoid is engaged, and the nut forward of that is the adjuster.

Note to others: this only applies to the D-type; J-types are not adjustable and you can't access the coil connections anyway.

We miss you too -- come up and visit!