"common" problems for a 2nd hand Si are....

*Distributor/fuel system would no doubt need rebuild/replace
*gearbox maybe in need of overhaul
*body wise....as most Si's are rare , old and no doubt been in a accident
*valves in need of adjustment etc

Really..the above are the same u woudl encounter in a car of the same age....and mroe problems on any other car type too

*BTW these have been my only problems ...in the Two Si's that i have owned.*

REMEMBER ! Give it a warm up...then after the oil has worked its way thru - it should be fine ! Rev ur heart out !