Mac C33 preamp upgrade

Hello forum. I have a Mac C33 preamp that I purchased new in 1984.  It has served me well in many systems over the years, although today it is not being used much. I’d like to put it back into service so I am wondering if there are any upgrades (high end caps?) that would improve the sound quality.  Suggestions and sources for the upgrades are welcome. I am aware of Audio Classics. Wonder if there are others. I did have it worked on 15 years ago by a highly recommended guy but he has since retired. Many thanks!