Stripped oil filter housing bolt

One of my bolts won't stay in, i suspect the threads are stripped. I've been running it with only two bolts for a couple years and not had any problems that I'm aware of but am going to change my filter and thought i should address it again. I keep an eye on the oil level because a little spits out and i top it off from time to time. I mainly just use it for plowing my driveway and chores, not trail riding. Any thoughts on a cheap fix? Also, how urgently do i need to fix this? Thanks in advance for your help!