Good news, and thanks to all for your kind help...
My 1990 420SEL has been repaired. The engine has had a major overhaul.
Originally bought the car for US$5,000, put about $5,000 in repairs and
upgrades, and now I have an awesome vehicle with about 120,000 miles on it.
A few years ago I spent $9,000 on a very nice 1995 C220 that had 99,000
miles on it but no rebuilt engine. It was good but not necessarily
reliable. I traded it in for a 2006 Honda Civic last September. Of course,
this 420SEL is leagues beyond the C220 (don't laugh). So I think I have a
lovely car now that will last for many years and is in great cosmetic shape
inside and out.
I read this forum several times every day to learn from those who share
their knowledge on Mercedes. This timing chain rail issue was a
catastrophic occurrence that could have been avoided, had I known in advance
of its proclivity to fail. I will appreciate anyone's further advice on how
to avoid breakdowns in my car's future.
Ron in Salem