Since Yaz joined the Sox in 1961, here are the fWAR leaders since then (51 years):
94.8 Yaz
70.8 Boggs
64.3 Evans
50.8 Rice
48.8 Papi
46.6 Pedey
39.4 Petrocelli
38.9 Nomar
38.3 Fisk
37.2 Betts
32.0 Reggie Smith
31.6 Bogey
31.2 Valentin
30.7 Lynn
29.6 Manny
28.9 Youk
27.6 Mo
25.7 Greenwell
22.2 Nixon
Top 5 by position: (Some players are counted in multiple positions)
C: Fisk, Varitek, Gedman, Vaz, Salty
1B: Youk, Mo, Scott, Gonzalez, Stanley
2B: Pedey, Reed, Andrews, Barret, Mantilla
3B: Boggs, Rico, Valentin, Youk, Devers
SS: Rico, Nomar, Bogey, Valentin, Burleson
LF: Yaz, Rice, Manny, Greeny, Beni
CF: Reggie, Lynn, Ellsbury, Burks, JBJ
RF: Evans, Betts, Nixon, Drew, Tony C
DH: Rice, Papi, JD, Stanley, Easler/Cooper
Pitchers
76.8 Clemens
51.9 Pedro
28.5 Tiant
27.8 Lester
26.5 Wake
21.3 Beckett
20.9 Stanley
20.5 Monbouquetta
19.8 Hurst
18.8 Eck
18.3 DLowe
18.2 Sale
18.0 Culp
15.6 Lonborg
15.3 Lee
15.1 Schill
14.6 ERod
14.2 Buch
14.1 Paplebon
13.1 Porcello
12.3 Siebert
11.9 Boyd
11.5 Torrez
10.6 Price
10.1 Radatz, E Wilson & Gordon
Overall with 35+ fWAR:
94.8 Yaz
76.8 Clemens
70.8 Boggs
64.3 Evans
51.9 Pedro
50.8 Rice
48.8 Papi
46.6 Pedey
39.4 Petrocelli
38.9 Nomar
38.3 Fisk
37.2 Betts