Sorry, I am not answering your question directly. If you go for aluminuim toerail, please DO fasten it with screws that are well countersunk.
I had an experience in a harbour in the South Ionian where we were moored in a bad storm. The stupid harbourmaster put us adjacent to a flat bottomed motor cruiser. At the height of the storm (Midnight through to the early hours) had me and my crew frantically holding off the mad bouncing boat in driving rain. The screws attaching the toerail on the side of this boat ripped the side of my boat down to the laminate in several places. One of the fender ropes was frayed so badly by one of the screws that we lost the fender. An absolute nightmare.
In the morning, the harbourmaster arrived with the owner of this cruiser demanding 500 Euros from us for the damage to the cruiser! Later when the authorities came to photograph the incident, I was asked "what damage". The damage to the cruiser was cruiser was the loss of three of these offending screws!
The outcome was a day arguing and photocopying insurance documents in the port police office. I refused to pay the demanded money and subsecuently informed my insurance company of the incident formally.
One replaced stanchion and gellcoat repairs done by myself was the outcome. My insurance no claim bonus was left intact.
Good luck with your new toerail and I hope you get the leak sorted out, but please bear in mind what stupid, badly fitted self tapping screws can do by way of damage to other boats.
