and dave easter wood said:

I've split cases on enough engines that have been sitting "only a few 
years" to know it would be time and money well spent.  One of those 
"pay now, or REALLY PAY later" deals.  In the "Best Possible Case", 
the oil has seeped down into the bottom of the case and broken down 
into a sludge-like mess.  
- - - -
yup yup yup.  been there

i look through old piles of engine for early 36hp or 25hp motors.  found a
25hp case in a junk yard that had been so badly corroded by old oil it was
garbage. holes eaten in it.  

the motor in my 53 was sitting at LEAST since 1966.   three years ago (27
years registration expired)  when i got it i took it apart, cleaned half inch
of sludge out of it,   got the case and crank measured, heads rebuildt,
 rebush rods,   new bearings,  new seals, new oil pump.   did i replace the
cam?  i might have found a cheap NOS german cam the right size i couldn't
resist.    i used different ps and cs.  finding standard 36/25hp main bearing
is not easy.  Basically put it back together.  And it purrs.   yum.  my first
complete rebuild.   :)