New to the forum this date. So much information on refinishing, thank you all.

I have T&G flooring made of Poplar that I installed 21 years ago. The finish I used was Gym Finish Clear Gloss manufactured by Bridges,Smith Company of Louisville, KY. Now after 20+ years there are some areas that need refinishing due to water damage. I'm not able to refinish the entire floor due to cost restraints, however I'd like to at least refinish an area of approximately 4 sq. ft..
I'd like to match the finish, however Bridges, Smith is no longer in business. I talked with the original owners son and was informed that the formula for the Gym coat was not available, but that it contained Petroleum Solvents.
So what do I use as a finish coat that would be the least noticeable of a repair?

I realize that quite a few eye brows are probably arched to the maximum over my choice of wood for flooring, however the spectrum of colors in the Poplar has been the focal point of my homes flooring. Yes it's a soft pine but if you're careful it can wear just as well as a hardwood.

I'll appreciate your comments and recommendations.
Poplar Guy

Depending on where you are located you may be able to buy almost the exact same finish that you used when you finished the floor before. An oil based poly-urethane will amber and help create the same type of patina that you have.
Remember that not only does the finish amber, but the wood itself is susceptible to ambering over time from light. Even in a room with no outside ultra-violet light you will see a diminishment of the red spectrum which oxidizes to become more yellow from light over time. If you would like to see a more perfect color match in the beginning you can add some powdered color to shellac and compare it after it has dried and then put another coat if necessary. Then you could cover the whole floor with a coat of water-based poly-urethane which will give an even gloss level and not amber like regular poly does after a few months.
It will be a guess for the intensity of any coloring scheme.
You would do well to coat the whole floor so it would be easier to clean. Scratches will harbor dirt and make the floor look gray.

Thanks Pete ...
An internet search came up with Lenmar Gym Floor Polyurethane Gloss Finish in Clear (1Y.809). Spec. sheet looked acceptable to me as a novice in floor finishing.

There's a dealer in Bowling Green who carries it so I thought on my next trip down to BG I'd stop by and have a look.

Idealistically I would like to do the whole floor rather than just a patch job on the water damaged spot. Perhaps I may attempt this at a later date this year, after I see the outcome of the repair.

Thank you for your input, it's greatly appreciated.
Poplar Guy