i assume your car is a V12, so I recommend you find a starter circuit for your model on the internet and view the components involved. The starter relay is a good starting point and to find the part on your car just ask the question again on the internet. Just look for loose or burnt contacts. You can short out relays to check them out but I would not go there if you not not sure what you are doing. If it is difficult to find components disconnect your battery and check all visible contacts. I know this looks to be a bit of an overkill but with old cars I think it is a good process to look for anything that can give you a problem in the future. I am sorry I cannot be more specific but I have not had this issue with my 3.6 cabriolet. My job before I retired was to do with domestic appliances and I found that with any electrical issue the first step to use is observation as a poor circuit problem will in many cases show some sign of deterioration, especially high voltage/amps circuits.