I've been through titling and registration errors for older vehicles several of times myself, most recently with a 1960 MGA last year.
Essentially, your task going forward is to tie the vehicle paperwork you have to the vehicle you have in such a way that your local vehicle licensing authorities will see fit to grant you new paperwork.
My suggestion is to try to obtain a copy of the datacard for your vehicle from Mercedes-Benz. Since your 230SL was originally a U.S. delivery vehicle, the Mercedes-Benz Classic Center in California may have the relevant data card. The datacard will contain BOTH the vehicle chassis number as well as the engine number. Other numbers will also be included, such as paint codes, and the body production number.
Once you have obtained the data card, you should discover that the engine number on your California document, on the engine itself, and the data card all match (except for the clerical error of an "8" being entered as a "3"). You should also discover that the chassis number on the frame rail, the data tag on the firewall between the hood latch and the data card all match. Finally, you should discover that the paint codes and body production number on the metal plate screwed to the bracket in the engine compartment adjacent to the edge of the left fender will match the information found on the data card. Additionally, if the original hood is still fitted, the last four digits of the body production number will be found stamped on the inside ledge of the hood near the left hand corner (raise the hood and look up on the underside edge at the left rear corner).
Hopefully all this corroborating information will help you convince your vehicle licensing authorities in Finland that your 230SL is indeed the same vehicle as identified in your California registration and subsequent vehicle importation paperwork and provide sufficient proof for them to issue documentation for the vehicle under its correct "113.042-12-0xxxxx" VIN.