I'm wondering what model you have. Have they been making the 618 that long? You'd think they would have tweaked some things if they had users complaining about a consistent defect. Although, 20 yrs out of your router is pretty good.
I have the DW618. I haven't seen a lot of comments. I saw a recent post/comment and asked the poster where he found the info. He only referred to a couple of sources. 20 years as a diyer probably doesn't compare to a daily user. FWIW it was fairly easy to replace the Magnet Ring and the shipping was more $ than the actual part ($2.99). I don't know how much a speed control unit would cost but it looked like an easy DIY repair.
From the comments I have seen a lot of folks use the DW618 in a router table.
I've got the 3 base kit (fixed, plunge, and D handle) and have used all 3. I have an extra fixed base and leave it installed in my table.
The only other routers I have used are an old Craftsman and a new Makita Compact so I can't comment on other brands in the DW618 (midsized) class. If necessary, I would buy the DW618 again.