No surprise there.
Does your dad have extension cords that are like 40 years old? Look like you just bought them? I mean coiled up so nice like you just pulled it out of the package? LOL My dad has extension cords older than I am LOL LOL. Still new looking.
So back to the engine, do you check the oil prior to mowing every time? I bet your dad did LOL.
Wondering if the engine was ran low on oil? Looks like a 1988 engine. There is a .020 over piston and rings available. Some parts are not though. Call a good mower shop and see if they can get the parts for you.
Or use this link to find your parts.
shop.briggsandstratton.com