Valve cover gaskets

[scout]

I have had the Valve cover gaskets on my 2002 WJ Overland with the HO engine replaced 4 times and it has always leaked. The mechanic has used different brands thinking that may stop the leak, no luck. I thought I would do the job myself I ordered the parts from Rock Auto as I always do and preceded with the task. I was conscious of the fact that the mechanic knows his stuff so what could cause this problem. After putting the new gasket into the slot I inserted the bush with new grommets. I believe I have found the problem the bush bottoms out before compressing the gasket to what I believe is acceptable. I checked the parts listing for the 2004 model and it has different part numbers to the 2002.
After all of that my question is, what is the difference between the two models does the later model have thicker gaskets than the early model. Has anyone experience this?
Thanks in advance.

[wjlimited]

My 05 wj overland has plastic valve covers, could that be the difference?

[scout]

Thanks for the feedback I was unaware of later models having plastic covers, do they have a groove for the gasket as the earlier models have?

[wjlimited]

There is a groove that the gasket sits in, but I don't know if it is the same shape.
The gasket isn't very thick so I doubt the later one is any thicker.

[scout]

The valve covers on mine where changed as one of the lugs was damaged so the mechanic had me track down another set which I did and he swapped them over. I dragged the old ones out of the shed and noticed that the spacers where shorter than the ones on my engine. This could be the problem as the gasket on the valve covers does not seem to be compressed. Has anyone come across this?
Thanks