Always better to use genuine mazda parts also if the oil leak is from the rear right hand side of t ht e engine it’s most likely the cam angle sensor o ring easy to fix.
I’ve yet to hear anyone say good things about pattern part cam cover gaskets, the general consensus is that they don’t seal properly and to use the genuine gasket.
There is no sealant between cam cap and cylinder head. The camshaft bearing surfaces are precisely machined and by putting sealant between them the bearing clearance will be increased.
The only places where sealant is needed is in the ‘corners’ either side of the camshaft/seal caps at the front of the engine and the CAS (cam angle sensor) at the rear if the engine.
I use Loctite 5699 sealant but other sealants are available that will do the job as well.
It’s a good idea to replace the CAS o-ring as well, they go hard over time and leak at the back of the head, all over the heater hoses underneath which then go soft through oil contamination resulting in them failing and a loss of coolant.
Regarding the crank oil seal I’d clean the area down to have a look, if you’re sure it’s ok I’d leave it alone. If you think it is leaking then change it.
If you do feel like changing it you may as well change the cam belt while it’s all apart and it’s good practice to change the water pump at the same time.
If the cam belt is covered with oil it would be a good idea to change it anyway.