sunsports didn't have fiberglass stringers until mid-'92...you can tell on '92 models if they have a curved windshield that they are the fiberglass stringer model. anything '93 and up has fiberglass.
as far as this one goes, that crack looks like the wood stringer on that side split or is rotted out. they are covered with fiberglass, but still wood underneath. if he'll let you, you can take a wrench to the motor mount bolts and try to tighten them a little; if they spin, the wood is rotted out.
'88 Sunsport, 2250lbs ballast, automated surf system, home made surf exhaust, surf flap, ACME 913, Krypt 6.5 HLCD's, Perfect Pass Stargazer
2007 Centurion Typhoon to be upgraded this winter!