Ford Fiesta 1.3 2002 Endure E Engine Fault ?

I've got. 2002 ford fiesta 65,000 genuine miles endure e engine , the problem is I think the engine is choking itself when it gets hot , car runs perfect when cold but when it gets hot it loses power and start tapering like theres no oil feed etc , I know this used to happen on older fords ( black death ) I had it n an old mk 4 escort once I took the drain plug out of sump knocked a whole In sump strainer and car was right again , any body ave any ideas if this could be the same thing ? I've checked breather pipes at front of engine and all seem clear , yet I take rocker cap of and it's breathing straight away through it so there must be a blockage somewhere ? Any ideas ? Done a diagnostic but no fault codes show up