We have finished in place bamboo flooring that really needs refinishing. Thanks to covid the original installers seem to be AWOL. The flooring was finished with a locally made urethane product, Diamond Lac, a Seattle company that is now gone.

We have wear-through in several spots that I would like to touch up until we can find/contact the previous installers. Can I sand down a bit in the areas that are abraded and touch up with another product to prevent staining and water intrusion into these areas? (In front of a fridge, under a garbage can). I have orbital, belt sanders, etc Any advice appreciated.

If you clean and sand to a fresh surface you can seal with Glitsa Sealer.
It is sold by the Rudd Company in Seattle. It is a conversion varnish that you add hardener to help it cure. A small area will not take a whole quart, so add the hardener proportionately to what you mix together. A chip brush which is inexpensive can be used one and tossed, but if you wrap it up in a plastic bag, and then in another so no smell escapes, you can pit it in the freezer and use it again without cleaning in lacquer thinner. Two coats with 150 grit sanding after the first coat is dry will give you a smooth surface, easy to clean. You can add more coats as you like. It will be glossy. If you want less shine, rub with 2/0 steel wool. You may need to get the finish from a flooring supplier. There is a finish for a final coat that you can choose from semi-gloos to matte. It is Glitsa Gold Seal.
I have been using this type of finish for 40 years and think it is the best!

Thank you for the reply. I looks like the product data says it may bring out grain of wood. Any bamboo experience? And since this is catalyzed product, any issues putting down next to the water based finish? And what sandpaper grit to use on old area that needs touch up. Any help appreciated

The sealer may not bother the water-based finish if it is the two part variety. This costs more and is resistant to more chemicals. If you try an area in a corner and it doesn't lift the existing finish you will be good to go.
To really clean the floor you need to start with 60 grit, but to protect it from more wear and stains use 120 grit. Apply two coats, the second as soon as the first one dries and you can hand sand and get some powdering to know its really dry.

The Ruud rep was kind enough to provide information for us. He had experience with Diamond Lac, the original coating. He suggests Glitsa NxG, single step waterborne product.
Any favorite applicators? Some have suggested Padco. Any info appreciated

Padco makes an 8" wide pad that can hold a lot of product. If you are careful along the baseboard and door casings, it can be the only product that you use to apply finish to floors. Attach a broom handle when coating the main part of a room. It works with water-based finishes or solvent based finishes. Work in an 8 inch wide strip from one wall to the other along the long edges of the strips. A puddle along the length of the wall can be spread like a snowplow from one side to the other. The last pass along the ending wall needs to be planned so you don't have too much finish on the floor...
If you are only doing touch-up, use a technique like an airplane taking off to end the puddle, feathering out the last few inches with almost dry pad.
A coat over the whole floor will make it all the same shine.

If you have wear-through in several spots on your finished in place bamboo flooring, you may need to sand down the affected areas and refinish them with a compatible product to prevent further damage. However, it can be challenging to find an exact match for the Diamond Lac urethane product used initially.

Before attempting any repairs, try to obtain information about the original product used and see if you can find a compatible replacement. You may also want to consult a flooring professional or the manufacturer of the bamboo flooring for recommendations.

If you cannot find a compatible replacement, you can sand down the affected areas and apply a new finish. However, the new finish may not match the surrounding areas of the floor, and you may need to refinish the entire floor for a uniform appearance.

When sanding the affected areas, start with a fine-grit sandpaper and work your way up to a coarser grit if necessary. Be careful not to sand too deeply or unevenly, as this can cause further damage to the floor.

After sanding, clean the area thoroughly and apply a compatible finish according to the manufacturer's instructions. You may want to test the finish on a small, inconspicuous area first to ensure a good match and proper adhesion.

Overall, refinishing bamboo flooring can be a challenging task, and it is always best to consult a flooring professional or manufacturer for advice and guidance.

If you like the deeper color of a solvent based finish I would recommend Glitsa sealer. If you do any sanding to bare wood and do not want the patch to show you will have the best results by sanding along the edges from wall to wall across the patch. You may not need to sand to bare wood all along, but you will see the results of your sanding where the patch is after one coat of finish/sealer. You could then sand a little more where the flooring still looks dirty so you come closer to match the good floor. The surface will darken when exposed to light so the patch ought to take a patina after a while. It could take a year.