[Furbabies mommy]

My cat classic tabby Persian Mr. McGwire is 17 years old strictly indoors weight currently at 14 lbs for a senior cat he is just awesome !! He has developed a gumball size lump on his cheek just down about 1/2" from his eye.
We had him at the vet 6 months ago when this was about 1.5cm in size it has grown almost twice the size now. The lump does not bother him at all, he eats very well and plays like a kitten a very happy cat.
The lump is not attached to anything it is free moving. When at the vet they suggested it is a calcium deposit and if it were to begin bothering him then we could consider surgery to remove it. We asked about draining it but they said it was not a fluid base. Other then growing in size from then it still does not bother him nor affect him in anyway, but the one change is when I was inspecting it a week ago I noticed a bit of a head on it like when we get a pimple so I gently squished it and out came a totally clear liquid, a whole lot of liquid, I kept gently squishing it until it was totally cleared out a good couple of paper towels covered in this clear liquid. The lump went flat and was like stretched skin, I cleaned it with peroxide and put some antibiotic gel cream that I had recently myself for a cut. I keep watch on it and routinely clean it. within 3 days it was beginning to fill again, I again drained it and again yesterday the same. There no puss or colouring to indicate any infection whatsoever. Today it is filling up again. Just wanting to get an opinion on what this could be. With the vet telling us 6 months ago surgery likely our only option and to now have fluid drain out I am thankful at his age we didn’t have surgery to remove it.
Is it possibly acne just like we get. I am concerned although it does not bother him or affect him and keep draining it I am ok with but why wont it go away. Appreciate any insight and info you may have with your opinion on this.
Appreciate your respond and thank you in advance. A concerned mommy