A very simple proof is presented of the fact that the Orr-Sommerfeld equation for flows that approach exponentially to a constant at infinity has at most finitely many eigenvalues. A completely elementary argument shows that the Orr-Sommerfeld equation has no eigenvalues when the product of the Reynolds number and the wave number is small enough.
Here is the whole article in the PDF format.
For my other publications related to the Orr-Sommerfeld equation see:
Here is a copy of the contents of volume 4,
and volume 3 of
Differential and Integral Equations.
You should not have problems finding Arch. Rational Mech. Anal.