We have an old house and the toilet does not flush as well as it should. Water comes out OK, but it doesn't always go down easily. I suspect replacing the flushing mechanism would help, but the toilet is on an un-level floor with the rear higher than the front. Using a level and a ruler its slightly more than a 1/4 inch off (3/8th, 5/16th?).
Is this enough of a distance to affect the flushing?
Is there a product to help me shim the toilet or do I need to make a shim out of plywood and a plane?