Sounds like something with the controller assembly went bad. I haven't actually taken apart my slim PS2, but the "fat" one uses a ribbon cable to connect it to the main system. You can probably still buy replacements for these, but it'd probably cost about 1/4-1/3 the price of a new console.
I'd just learn to live without it. I find I rather like not having it, though I disable it because I have a cordless controller and it's to prolong battery life.
for a while now i have not had any rumble in my multiple controllers and games with the there rumble options all on. I tried my controllers and games and memory card at a friends house so now i know this problem has to do with the ps2 itself. How do i fix my ps2 to get the rumble feature back into my games. any help will be apreciated

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic