Need help reassembling the original radio from an 1985 GSL SE. Hoping to add a line in. Any suggestion on where I can take it to get it done or anyone out there who can do it at my house. The car is located in Kitchener, ON.

 

There's line-in kits that just plug into the antenna lead (I don't know how well they work, but I've heard of them).
Look up local electronics repairs via Google or kijiji. There's not a lot of places that fix car stereos anymore though, not worth it when your 30 year old head unit could be replaced with something much better for $150 at Walmart/Canuck Tire/Future Shop.