why is air coming around rear seal.

this is a 125g1 model which as been sitting for 2 years and was not serviced in 4 years. it used to build and maintane 80 psi no problems and when started this year it will build 40psi but when used drops to 20psi.when you cut it off and listen you can hear air blowing past rear engine seal and is leaking oil front and rear seals. is this just stuck rings on the pistons or something else.thank you for any help you can give. its old but would like to use it for a little longer. have lawn service and only use it maybe 2 weeks a year to blow out irragation systems for the winter. Kenny, Bangs