I have the same Rand 4000 5 HP compressor in my home shop. Mine cost something like $200 but had a nearly new Marathon motor. It works great for my use, although it is a little loud.
Bad news is that IR no longer supports parts for this unit. The lady I spoke with said that they sold all the obsolete parts to a dealer in, if I recall, Bensenville Illinois. I think it is on or near Rte 83. I picked up some parts in person, as I lived near there at the time.
The place was called General Air Compressor and the guy was named George, but this was probably 4 or years ago and I don't know if they are still around.