It should be a 4L60E for that year.

There is actually a seam on the head itself on my 3100. It took a headlamp and magnifying glass to see it. It can be separated with the help of a razor blade. From there the blade drive can be disassembled by using a needle nose pliers to move the tension spring to each respective side. Upon disassembly I do not see how these blades are self sharpening but the assembly of mine was heavily impacted with tiny beard stubble that may have been affecting the sitting tension on the blade drive assembly. I thoroughly cleaned it and reassembled it and am now running it through a battery cycle to see if it'll sharpen the blade. Time will tell. Hope this helps someone. I know it's an old post.