A line broken by white gaps almost always points to a disturbed supply of paste and not to a defect in the pen. Conventional ballpoint refills work with the help of gravity: write standing up, overhead or against a vertical surface and the flow of paste breaks off, leaving the ball running dry. On building sites there is the added problem that fine dust from the paper is turned into the ball socket and impedes the flow still further. The line width makes no difference to any of this.
The remedy is a pressurised refill of the Fisher Space Pen type, which is also made to fit Montblanc ballpoints. These are pressurised with gas and write whatever their position, overhead included, and in cold or dusty surroundings. Ordinary shops hardly ever keep them in stock; supply is arranged through Standardgraph, Fisher's German distributor, which will also say which specialist retailers are nearby. Wear to the gold plating at the tip is normal with daily use and has no effect on how the pen works.