Yay! A result.
Steve, these plugs are usually exceedingly difficult to remove, they were punch-locked around the diameter in the works and even if that is ground back they will still put up a fight. By which I mean to explain that if one has come out, it is probably because someone previously removed it, possibly damaged the thread, and the new plug for one reason or another was not a proper fit. With this in mind check that your new plug fits well, clean the threads with solvent and use some suitable Loctite on it. If necessary tap slightly oversize to repair the thread.
I'm pretty sure the hole in the case is BSPP, you can use a BSPT plug or BSPP if it is sealed (preferably with a flange). Doesn't really matter as long as it does up tight. Any old-school plumber's merchant should be able to help you out. Be wary of stuff from China which is usually not BSP at all but NPT, which is 'similar'.
Steve, these plugs are usually exceedingly difficult to remove, they were punch-locked around the diameter in the works and even if that is ground back they will still put up a fight. By which I mean to explain that if one has come out, it is probably because someone previously removed it, possibly damaged the thread, and the new plug for one reason or another was not a proper fit. With this in mind check that your new plug fits well, clean the threads with solvent and use some suitable Loctite on it. If necessary tap slightly oversize to repair the thread.
I'm pretty sure the hole in the case is BSPP, you can use a BSPT plug or BSPP if it is sealed (preferably with a flange). Doesn't really matter as long as it does up tight. Any old-school plumber's merchant should be able to help you out. Be wary of stuff from China which is usually not BSP at all but NPT, which is 'similar'.