Before you rip it to pieces, which tamper are you using? Im not saying this just cos I sell them, but using the built-in tamper its impossible to pack evenly, so youll end up with low pressure areas which will always cause quick and overextracted shots.
You should be aiming for roughly 60ml of espresso from a double basket into a single cup in about 25 seconds. Its not magic, but use that as your initial goal. 12-18 seconds sounds too slow, so if youre getting those times and it still looks too pale Id suspect the tamp. What do the streams look like from each spout? Are they individual drops of espresso, or drop / stream / drop, or thin streams, or thick streams? What about the colour?
Ive not tried to remove the grinder before, but Ive had mine for 4 years and have never seen the need to change them. I suspect unless yours has had much heavier use the problem lies elsewhere.
When I pack so tight its hard to get it in the group, with a correct grind it almost always chokes the machine. I normally use about 2.5 7g spoons of beans in the hopper and grind that into the basket, and once tamped its about 5mm below the top of the basket.