o. . Murray Sheet Metal Co., 967 F.2 980, 984 (4th Cir.1992) (opinion work product "absolutely immune" fro discovery); Nutramax Labs., Inc. r Twin Labs., Inc. 183 F.R.D. 45 , 462 (D.Md.1998) (under Fourth Circuit case law opinion work product has [been] characterized variously as "absolutely immu