Your erratic manual control is probably because your glass panel is loose and not sitting in close proximity to the sensor system.
I use superglue to stick the glass panel back to the plastic carriers. I've done loads of them and it works every time. Avoids the problem of removing the existing foam tape. Just run some superglue along the existing foam and hold the plastic frame in place for 30 seconds or so and job done.
The manual is not on site yet but peter has a copy on his site. Send him a PM and he will send you the password to download.