The furnace in my garage is slowly dying

I have had the worst time trying to heat my garage… I do a lot of work in my garage, so I like to have it at least sort of moderate in there.

I care about it to be around fifty degrees in the garage. It is the perfect temperature while I am working. It does not feel too moderate or too cold, however at first, it is a little chilly, however once I beginning working it feels perfect. I have a big propane space furnace in my garage that I have been using for the last couple of years. It is the only furnace that I have found that keeps the garage around fifty degrees. It is still a pain because it takes about three hours to heat the garage to that temperature each afternoon, although I believe it is worth it in the end, and unluckyly, my furnace is not doing well. I have made sure that the propane tank is full, and I have tried everything I can to scrub the thing, however it still is not working right. It just is not putting out the heat that it used to, and it is getting harder and harder to ignite. I have thought about replacing a few parts like the thermocouple, however the furnace is so seasoned that I figure I should legitimately just go ahead and buy a whole modern one; My spouse told me that he would buy a modern one if it was him. I have been looking at a few weird stores and online to find the cheapest locale to buy a modern one; Thankfully, they are not legitimately extravagant, so I should not have any problems either way.

furnace/heater