Browny black deposits on pistons and head gasket weeping

[xy500]

G'day

i'm posting this looking for some advice; I have a 1971 Ford Falcon 500, with the 250 ci inline 6, the car is dual fuel but i mostly run it on LPG.
While i was checking the spark plugs today i had a peek at the piston and it had these funny deposits on them. I've seen the normal carbon deposits associated with old engines, but these were kind of half black and half brown, really speckled and only in the middle of the dish of the piston. here's a couple of photos (though you can't see it much)

i was wondering what the significance of these deposits was, and whether they should be worried about and if i should bother trying to remove them.

i also notice my head gasket appears to weep a very slight amount of coolant towards number 5 and 6 pistons on the spark plug side of the engine; it has been using a little coolant (maybe 3-400ml every few weeks) though the engine doesn't really run that hot and runs fine with no smoke from exhaust, no oil in coolant and no coolant in oil. should i be worrying about this?
i only use the car to get to uni and back, and i plan on rebuilding the engine when i finish uni and get some money together, so anything that i can baby through i'm not going to bother fixing right now

thanks for your time and help!
colin

 

[SONNY]

does look a little strange.what did the plug look like?

 

[xy500]

hey thanks for the reply
the plugs had what looked like black deposits with some light fluffy tan deposits on top of the black stuff. there was some yellow deposits on the insulator, i think i need a cooler plug.

 

[XPC66]

The ash is a classic sign of lean burn, insidious knock, not cold enough spark plug, overly advanced spark. Eventually you'll end up with a hole in the piston top.