I topped up the oil in my '98 Cinq engine (899cc) and noticed a faint exhaust smell in the dip stick oil. I do have a small oil leak at the oil pan seal but it hasn't caused any bother. The exhaust is clean so I'm not burning oil. But this exhaust smell in the oil does bother me; I'm concerned a seal inside the engine may be failing.

Any help here?

there should be a rubber tube from the rocker box cover to the intake or/and throttle body. The end at the rocker box will have a trap or restrictor which can become blocked.

Leave end of tube overnight in kerosene to dissolve the gum

My breathers gum regular on several different autos.

I'd not worry overmuch. It's quite natural for some exhaust by-products to find their way past the piston rings. No seal is perfect.

A dry and wet compression test will tell you pretty much all you need to know about the state of the innards of your engine, but, warm the engine up, find the breather tube of which Pep0 talks, with the engine running remove one end, and, if you can see gases, it points to worn bores.

yes worn bores or worn rings will create more crankcase pressure but the breather can block independent of excessive wear you may need to keep clearing it if it blocks.

for example could be too many short trips.

I've needed to replace rings after 70k miles on low compression but that was on a engine that did not show breather symptoms.