Back around 2003, I picked up a Paronelli. Nothing fancy, but it's sentimental; it's been around the world with me (including 3 trips to the middle east). About a year ago, it disappeared. I searched high and low, and could not find it. Eventually, I found the stem, but not the bowl. Yesterday, I found the bowl under a piece of furniture. I'm going to guess the culprit is a cat...lol.

Long story short, it's seen better days. The stem is solid, but it's two pieces with a metal decorative spacer. The 3 pieces were all one when I purchased it. I contemplated cleaning them up and trying to re-glue them. I also considered a replacement stem.

For a ~20 year old pipe, what kind of maintenance/refurbishment would you recommend?

I have bought some estate pipes, most in good shape. For my peace of mind, I soaked them in a cheap whiskey to clean/sterilize them.

All the answers are here:

Pipe Smokers Forum

I'd see if I could send it to Paul's Pipe Shop in Flint, MI.  They still manufacture pipes in the basement and are capable of completely restoring almost any pipe.

I have really good experiences with Rich over at Briarville. Refurbed and hand cut a new stem for a sentimental Jobey that belonged to my grandfather. Also does all my estate pipes. I believe he recently became the official USA repair shop for Dunhill pipes.
Briarville

https://rebornpipes.com/

I enjoy reading this guy's refurbishments, some good ideas too