I agree with Tony H that the 189 engine can be very expensive to repair if its fundamentals are not sound. You should have an experienced mechanic thoroughly check it out.
As for the air suspension system, it, too, can be expensive to make right, but is amazing and durable once sorted out. There are several sources for rebuilding leaking control valves (one rear, two up front plus the main distribution valve...), which is the most common problem.
Rare car. Only 2369 made world wide. How many sound running examples are left now? Probably a handful at best. Remember, this is the same basic engine that powered the legendary 300SL.
It has mechanical fuel injection.

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Berfinroy in CT
Present vehicles:
1973 300 SEL 4.5
1959 Rolls Royce Silver Cloud I
1973 Citroen DS23 EI five speed
Past vehicles;
1959 Thunderbird convertible/430
1958 Bentley S 1
1976 ex-Max Hoffman 6.9
1970 300SEL 2.8
1958 Jaguar MK IX
1961 Jaguar MK IX
1963 Jaguar E-type factory special roadster
1948 Plymouth woody
1955 Morgan plus 4
1966 Shelby GT350H Mustang