Petcock issue

[Kevin Hollis]

I'm getting intermittent stuttering and loss of power which I think may 
be a clogged filter in the petcock.

It's probably been on there for a good few years.
What problems should I expect when I open it up ?
Will I have to replace the rubber diaphragm ?
Will I need gasket sealant when I bolt it back up ?

I'll probably take out the filter and replace with an in-line version.
Any problems with this plan ?

Thanks
Kevin

PS
Put on a new Motad exhaust last weekend that I snapped up for £225 on ebay.
Lovely note, nice and bassey at low revs. Needed a bit of angle grinding 
to fit
around the oil filter though.