try rocol flawfinder you can find it on flebay or in any good enginnering shop its a 3 can system works well and shows up any cracks

can 1 Flawfinder Safety Cleaner

Prepares surfaces prior to testing
Removes contaminants, oil, grease, dirt, excess penetrant
Safe on metals and some plastics

can 2 Flawfinder Dye Penetrant

High definition red dye indicates surface cracks and flaws in normal light
Water washable

can 3 Flawfinder Developer

White film which highlights penetrant dyes
Excellent background for viewing
Water washable


hope this helps

dooge