I agree that the opti is most likely the problem . water is a killer to these. some of you down in texas got some flooding rains lately. you drive this is deep puddles it is N/G..My caprice lt1 cranks but will not run I replaced the spark plugs ac delco 2 weeks ago because it did the same thing when it rained. the car was running fine no hesitation. The other day it rained heavy I go to start it it just will not run I pulled the plugs are drenched with gas I also noticed smoke from the throttle body .I replaced the ignition coil eariler today. and it still didn't run I running out of ideas can someone please tell me what else I should check for.
The other issue is the plugs being fouled, and this excess fuel getting into the crankcase.
remove clean dry out OPTI , clean and/or replace plugs. then with the water pump off see if it runs for a few seconds. then put it back and if it works out change the oil.
if you see any oil leaking behind opti replace the seals felpro front cover seal kit.