I now have a new unfinished red oak hardwood floor installed in an apartment
that I will be renting out.

What I want is a truly CLEAR finish to put down on the new unfinished
flooring.

I have extra flooring that I have set up so I can test various finishes. I
have already tested a number of stains and, if I have to, I will go with one
of those. But, what I really want is to be able to put a completely clear
finish over the new unfinished hardwood flooring. I like the way it looks
now and I would like to be able to keep that look and coloration. All of
the so-called "clear" polyurethane finishes I have tried so far are not
really clear. They are amber color, and they also stain and darken the wood
grain.

Here are my two questions:

1) I am interested in clear Moisture Cure Urethane (one brand is made by
Garco) -- but I can't find anywhere to buy it. It is supposed to be truly
clear. I know it is super volatile and maybe that's why it is not easily
available. I can apparently buy it online, but then I have to wait 4 to 14
days for it to arrive. Does anyone know where I can go in person and buy
this stuff? I am in New Jersey near Philadelphia, PA.

2) I haven't tested out water-based polyurethane products yet. I get the
impression that they can be more clear than oil-based polyurethane. MinWax
sells a clear water-based base coat and a clear water-based polyurethane
that goes over the base coat. The clear base coat is supposed to seal the
tannins (or something like that) in the wood so it doesn't darken, and then
hopefully the top coat won't darken the wood when it is applied.

Are water-based polyurethane finishes okay for hardwood floors? Are they
durable enough compared to oil-based polyurethanes? Are there any special
cleaning requirements or instructions for water-based finishes that are
different than for oil-based polyurethane finishes?

Can I later cover a water-based polyurethane finish with an oil-based
polyurethane finish? I think the answer to that one is "no", but I thought
I would ask anyway.