I'm no help with that particular GM1000 model, but go here
and click the first link to download the model/serial number range specific Operator Manual and Parts Catalog for your mower. The model and serial number should be on a plate attached to the mower frame. I'm guessing it's an 04051. The Operator Manual has a section that discusses adjusting HOC.
If you find that you have parts that are seized or broken, it looks like you can still get those parts from R&R here
. Just please double check your mower model number - I'm assuming it's an 04051. :thumbup: