Seepage

It has a seepage.

[…] while they all admit that the most serious losses occur by seepage of gas from, and oil into, the combustion-chamber and that this seepage is […]

In the case of the Rio Blanco experiment, it is the seepage of gas which is considered to be the "worst possible situation" that might occur.

Despite some seepage of customs from north of the border, the Day of the Dead is not [widespread in the US].