I did the same thing...block heater just stopped working. I had been plugging it in for long periods, and it must have had enough. I tried a lower radiator hose heater for quite some time, and it did work for the most part but NOT like the block heater. I couldn’t find a proper block heater locally so had to use the lower hose heater type to get by for the rest of the winter. I ended up installing a used block heater from a spare turbo 617 engine I had. I did the swap (6 +years ago)when I had the turbo off the following summer when it was nicer out. I still plug my old swapped in block heater for long periods and it’s still fine. We regularly get stretches of -30 Celsius or colder up here and the block heater is the way to go. I actually still have that lower hose heater installed so I could probably use both but I have never had a problem with just the block heater.