40 wt. oil in rear shocks

["Paul J. Burr" <tigerpb@ids.net>]

Whilst reading the Kastner comp. prep manual, I noticed his recommendation
for using 40 wt. racing engine oil in the rear shocks.
Anyone done this on a street driven TR6? How is the ride quality?
 My rear shocks have the resistance of a marshmallow and I was hoping that
replacing the oil would be a cheap alternative to replacing them. They look
clean, no visible signs of oil leaks.
Paul Burr
'74 TR6