Lately the oil train has become unreliable: in a sequence of maybe 20 runs around the railway (perhaps 300m travelled over a lot of points & bends) a tanker will derail. That then blocks the whole railway, because it happens underground.
The Virgin carriages have a weight of 27g each. The oil tankers are only 11g, so I decided to add some lead weights (aiming for 13g each tanker). The tanker body is clipped together - no glue. The end caps can be prised off using a scalpel; thereafter the body simply opens up.
Lead sheet is readily available from DIY suppliers (it is used for roofing) and two pieces approx 10x25mm each weighed 6.5g. For them into half circles, and glue them inside the ends of one half of the body (I used Uhu). The reassembly the body by clicking back together, and all is done!