I would do the same if I had a vacuum gauge. But rather than buying a device that I will use, maybe only a few times, I'd rather disassemble the vacuum pump and replace its seal.
You're right, it's not that expensive - check out our sale, you can find it for £8. However, I already got to the vacuum pump) there was a lot of oil in it. this is normal? Anyway, I gave it a good wipe down, blew it through with cleaner and put it back together. I couldn't find anything that would prevent it from working.