Top Sash guides

I need to replace a broken top sash guide, and it appears that the correct part number is #18-009. All the dimensions check out. The latch on my window says "Viking" but that is the only identification. The photos are of a "good" piece. The bottom screw on every window is a Phillips-head. The top screw appears to be either a torx-head or an Allen-head, but in either case, on all windows, the head appears to be buggered up (evidently by the manufacturer, either intentionally or due to poor workmanship); I cannot remove it with either type of driver. What do you recommend? Can I just drill it out, or is it holding the window together? The window seems to work okay with only one operable sash balance.

Thanks, Bob. Subsequent to my post, I discovered I had several of these sash guides as spares from an order I placed with Swisco several years ago. I also took a closer look at the top screw on the broken sash guide (not the one in the photo) and determined that it was not badly boogered up, and that it was a Phillips head. I was able to remove the screws and I replaced the sash guide and now I am back in business.
Several of my neighbors have replaced all of their windows (same builder), but thanks to Swisco and my DIY leanings, I have kept my windows in working order at very little cost.