"\@startsection" --> "\scr@startsection"

kalibrierschein.cls

@@ -9,7 +9,7 @@
 \newif\ifnoCMC \noCMCfalse
 \NeedsTeXFormat{LaTeX2e}[1999/12/01]
 \ProvidesClass{kalibrierschein}
-  [2022/04/26 v0.6e documentclass PTB `Kalibrierschein' (RN/PTB)]
+  [2023/05/08 v0.6f documentclass PTB `Kalibrierschein' (RN/PTB)]
 \DeclareOption{BS}{\def\ks@location{Braunschweig}}
 \DeclareOption{BLN}{\def\ks@location{Berlin}}
 \DeclareOption{KK}{\edef\ks@kalType{\CurrentOption}}
@@ -377,7 +377,7 @@ footskip=0bp,
 \pagestyle{scrheadings}
 
 \renewcommand\section{%
-  \@startsection{section}% name
+  \scr@startsection{section}% name
   {1}% level
   {\z@}% indent
   {-3ex \@plus -.5ex \@minus -.2ex}% beforeskip (abs.!)