1990 ES250 Spark Plugs

[Entropy]

Hi guys and gals,
Newbie question(s) for ya. I'm servicing a 1990 ES250 for a lady in our church. I already found a post that told me to pull the upper intake plenum to access the back spark plugs, done. How about replacing the upper plenum gasket? Do I need to purchase a whole intake set or can I clean the old one up, assuming it stays in one piece, and just use a spray type sealant?
2nd question. I tried to pull out the diagnostic codes frim the ECM, I got a contiuously flashing check engine light, about once every .5 seconds. Is this an all clear signal?
Any insights and ideas are appreciated.
In Grace, Entropy.

[BadChicken]

You probably should replace the gasket but doesn't have to be
As for the codes, when they start flashing then you have to follow the pattern
example c c c c c c c represents 34
c c c c = 12
they will blink fast and then a pause and then fast again to represent the first and last digit of the number
but watch closely because it may have more then 1 code in the memory
hope this helps