I was cutting grass and my mower locked up. I thought I had hit a hole with the front wheel, but had not? The Transmission oil was low but not out. The transmission never made any noises or slipped? I added 5w 30 to the full line. Cranked the mower. It won’t go forward or reverse? This transmission has been super with no prior problems. Would this definitely be the transmission? If it is where can I buy a new or reconditioned transmission? Cost?