An Army private who went absent without leave after returning from the Persian Gulf War received 30 years to life in prison Monday in the robbery-murder of Los Angeles TV news engineer Jeff Webreck.Superior Court Judge Lance Ito sentenced John Louis Rex, 23, of Burbank to 25 years to life for first-degree murder plus five years for using a handgun in the slaying of Webreck. Rex pleaded guilty last month to killing Webreck, an engineer for KCOP-TV, and burying the body in Angeles National Forest in September 1991. Ito refused on Monday to allow Rex to withdraw the plea, which Rex claimed he made under the strain of solitary confinement. Webreck, 44, of Glendale, disappeared after leaving the Channel 13 studios in Hollywood on Sept. 4, 1991. His body was found three days later. Rex was reported absent without leave from an Army base in Oklahoma in July 1991. He turned himself in at Fort Irwin near Barstow six days after Webreck’s slaying and was arrested. Rex and a brother-in-law used Webreck’s stolen credit card to purchase clothing and electronics equipment, authorities said.