Russ Jackson wrote:

How rare is this typewriter?

Close to a million of them were made, and plenty of examples have survived, so from a North American's perspective it's not at all rare.

Russ Jackson wrote:

Should I take it apart or leave it in as is condition?

Why would you want to take it apart? Do you have experience with tearing down machines? If it's working properly, and it's clean, I'm not sure why anyone would want to disassemble a typewriter other than to alter it in some way.

Russ Jackson wrote:

Have you ever seen chrome feet on an Underwood of this era?

No, not that I can recall, but looking at your photos I doubt that they're original to the typewriter.

I'm pretty certain that your typewriter is an example of a rebuilt/refurbished model given that an early '30s Underwood should have smooth paint. Considering the cost of typewriters back then, it was common for manufacturers to refurbish and resell older models, and those machines were often updated a little, particularly their paint.

Your Underwood looks to have been previously owned by someone who probably did a little "restoration" work of their own, and who might have decided to chrome the otherwise bland looking feet. The worn decal on the back of the machine and the state of the spacebar belies the seemingly pristine condition of the typewriter; this is not a typewriter that is in exceptional original condition, but one that has been worked on a lot to create that illusion.

Russ Jackson wrote:

Were there different levels of Model 6's?

I'm not certain what you mean by levels, but there were different features available such as the tabulator and carriage width. If you were referring to aesthetic finishes, I don't think so.

Russ Jackson wrote:

Any guess no the value?

It would depend on where you live, how you're selling it, the day of the week, and who happens to be interested in it. For example, for me it's a clean, refurbished Underwood 6 and I would never pay more than $75-100 CAD for it. The wealthy person walking behind me at the antique market might not know a thing about typewriters and might want it as a prop for a bookshelf and think $400 is a bargain. In short, its value is what someone is willing to pay for it. I regularly come across $50 typewriters being sold for $500, and they're being bought by those who don't know better. It's the reason why a large number of typewriters being sold in my area are those being flipped by middlemen who don't add any real value to the machines they're selling.  
 

I'm about 100% certain this has been refurbished -- and the crinkle paint is a dead giveaway, along with the simplified decals and the keytops, which are of a later vintage than the machine (more like early '40s). Also look at how some of the screws on the sides of the machine have been painted over -- Underwood would have painted the frame before assembling it. Check out the Typewriter Database to see what the machine looks like.

And I agree with Uwe about the feet. My 6 came with thick black metal spacers (1/2") between the frame and the rubber feet. But I like the chrome -- and I love the way your machine looks overall.

I also agree with Uwe that if it's working fine, don't touch it beyond trying to clean it up a bit. 

Where did you get this machine? Your mention of it having been covered in something like Cosmoline indicates it was stored away carefully -- like by the military. I am sure that was a real hassle to clean up, but the stuff did its job, as you said. Looks like the platen can stand some further cleaning.

As for the space bar, I'd like to think some sort of epoxy or Gorilla Glue would mend it well. Maybe others can suggest the right stuff to use.

It looked horrible but I was pretty sure it was a film so I rolled the dice.