There is some good advice here. A few things come to mind, you may want to ask the previous owner. How often was the oil changed? What type of oil sender is he using? How many miles on the engine? What weight of oil was he using when the problem arose?
The oils we have today don't sludge like they used to. I would take DanielC's advice and run it. Once you can take a look at the pan you will know a lot more about the engine.
"When I was younger, I could remember anything, whether it had happened or not." - Mark Twain