Considering buying a 1990 300 SEL, nice car, milegae is around 113,000. Two owner car, all records. Checks out ok except there is a clicking (light tapping) noise from upper front of engine. sound appears to be cam or valve train related. Any ideas? Any pitfalls in this model? I am not too familiar with them, more at home with '70s 280 SE 4.5s.