If it took 15 mins for ANYTHING to leak down 3mmHG, that's a non-issue. Anything big enough to cause idle or running issues is gonna be something big, as in won't even hold vacuum for 1 second.

Be aware that the 90s W124's are known for biodegradable wiring harnesses that crumble and cause all sorts of weird issues.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]