2001 S40 key stuck in admission

[markway]

Have gone through a lot of problems since buying this Volvo in 2006. It now has 120k miles on it, and at the last oil change the mechanic at the dealership showed me that sludge had built up around the oil filter and warned me that the engine could quit any time. That happened tonight. I stopped at a store, and when i went back to start the car the key would turn but nothing happened. I turned the key back and forth a few times and it eventually stuck in the on position. So I had the car towed to my mechanic to take a look at on Monday. In the meantime, with the key stuck in the on position the battery is running down because the lights are staying on. I am hoping there may be some way to do an engine flush and maybe switch to synthetic oil. If replacing the engine becomes the only solution then I am going to be looking for the least expensive source for a replacement.

Any comments appreciated.