Do you have a part number? I wasn't sure which plastic you used.
I use the Smooth-Cast 60D, this is a semi-ridgid plastic 50/50 mix. It is still soft after it comes out of the mold, but after 72 hours it is hard like ABS and not brittle at all. I also use the black So-Strong color tint to make it black. The natural color is clear amber.
Here is another thing I like to use it for, this works great for those wet areas. Using the Smooth-on OOMOO-25 liquid rubber, I make a rubber mold that can be used over and over.
Picture of the wood negative mold and resulting rubber mold, in it you can see a bad spot on the rubber - this is from not mixing it good so be sure to stir it well, but it is OK for this application;
Here you can see the circuit board sitting on top of the stand-offs I designed into the mold.
Now, if there is anything you don't want the plastic to flow into, cover it with clear packing tape, like those green connectors.
Then I mix the 60D plastic and mix in some color tint. First I pour some in to make sure it gets completely underneath the board, then I set the board onto the stand offs and finish filling the mold.
De-mold time! it peels right out.
Then I clean up the edges on a sander, drill 2 mounting holes and vola! a water sealed circuit suited for mounting in an engine compartment.
I should have the box demo done this weekend, I got a good start on it.