+++++++++++As Mike said no details. If the lock is on top like mine,the part that locks on shaft was broken.The part is no longer available from Sears. I dug thru my junk and found a nut that matched threads colet. I cut it down thin enough so when screwed on above colet nut and jambed tight to end of shaft threads ,it does not get in the way of tightning colet nut. You have to hold top of shaft where lock is broken to jamb nut so it will not spin off when tightning colet on bit.
Welcome to the Router forums.
You don't say what is wrong with the spindle lock but I figure it jumps out of the slot when you try to tighten or loosen the collet nut. If this is what is wrong then you can file the lock plate so the shoulder has a good flat surface to match the slot. To file it you will have to take it apart. Be careful and don't let parts fly out. There is a spring but if you watch what you are doing you'll be alright.
When you put it back together make sure the spring pulls the spindle lock out of the slot. If it doesn't, start over again until it does.
I have one that needs that done to it and tomorrow would be a good day to fix it. I'll take pictures as I work on it and then make a post on this easy repair.
Hope this helps,
Work safe, Have fun, Cut some wood,
Actually, after some dinking around with the red plastic...putting some leverage on it...it did pop into position and functioned appropriately. So, I can use it until I break the plastic. There must be a way of removing the red plastic slide handle so I can clean/lub the interior mechanism, but I don't know how to accomplish that. I fear breaking the plastic. I'd appreciate any tips.The red in/out/slide lock you discribe is exactly the lock like I was writing about. when I took the top apart ,the lock surrounds the shaft and slides to anarrow cut out to lock.The slide was split and is no longer available from Sears. If you have ?'s post. I will check back.