Reel problem

[MississippiBoy]

I have a BPS Pro Qualifier reel that I bought off eBay a couple of years ago. It works fine, except for the fact that it doesn't engage the spool when you turn the handle after making a cast. To engage the spool, I have to basically hit the handle with my hand as I start reeling. I've taken it apart, at least as far apart as I'm comfortable with, and cleaned it up, light oiling, a little grease, etc. But it still won't engage.
If I don't pop it with my hand, it makes a clicking noise, like it's trying to engage, but it stays in freespool, and I can hear and feel gears slipping past each other while I turn the handle. I hit the button again and pop the handle, it works fine. But I have to bump it for it to engage. Anybody got any ideas about what to look for to fix it? Thanks.