I agree that the marine apartments was a possibility where the car was parked up. The reason I'm not ruling out the links car park is due to the fact it is literally pitch dark and nobody at that time of year would have been using it. Even had he came out of the links car park and turned right he would not have been seen from Alistairs House as the havelock Hotel and the braeval Hotel would have been blocking his view. He wouldn't have necessarily pulled out of the car park turned right past Crescent Road, instead he would have joined marine road straight away with crescent road just of to his left where he could turn into , but clearly he would have by passed that.
The only reason I'm skeptical about the marine apartments is due to the fact he could have risked been seen running on the pavement heading towards the car park there, it's also very well lit up (the car park) and he could have been seen by residents who were staying there. But again I'm not rulling it out.
For me you can look at both sides of the coin, would you be more suspicious witnessing someone pulling up infront of you in a car where the drain is located? , and spending a bit of time there - in hope that nobody see's you dumping the gun? . Or do you spend a little bit more time quickly putting your bikers helmet on in a pitch dark carpark where there is nobody about then drive to the drain and discretely dump the gun- and avoid any unnecessary attention to yourself or risk been seen by another driver/ pedestrian acting suspiciously?
If he did use a car then I can only assume due to the fact that the gun was found on the passengers side of the car, that he must have had an accomplice driver with him.