Hi. I have a +/- 20 yr old model that we need to reset. I know that past code, but, now am having problems getting it working. Not sure if we did something to it or not. Model #8500.51 We also have an Access code for it. The battery started leaking acid, we cleaned it out, and now it works, but we can't seem to use the code we've always used. The previous owner of our house did not give us the manual for how to change the code. Can you help us? Thanks in advance Joanne