Your newest car is 12 years old - your newest Benz is 19 years old. You have to expect to do repairs on cars this old - you are going to have some time periods where you have to do LOTS of repairs on your fleet. Its the nature of driving old cars....

I have gone thru periods where I have been bombarded with repairs and then have had nothing go wrong for a year. On the other hand its possible you may have to face a similar set of repair tasks next month.

Going thru periods of lots of failures can be stressfull for the home/hack mechanic - especially if you have lots of family/work commitments.

If you don't enjoy working on these old cars I would trade in one benz and the volvo and get a Camry or Honda that is a couple of years old. This way you will have one car that should not require any major work for at least a few years. Reducing the number of old vehicles should relieve your need for multiple repairs on multiple vehicles.

Tim